scripts: dts: dtlib: improve formatting of long arrays

Split long arrays into multiple lines to improve readability of the
output DTS file. A new line is started when the array data exceeds
80 characters.

Add a few test entries to verify the new behavior.

Note: the F821 linter suppression prevents flagging 'array_start' and
'array_newline' as undefined variables. This is because these variables
are initialized when an opening brace is output, which is necessarily
before any element in a byte or prop array. A sequence of markers not
following this pattern would indicate a bug in the DTS parsing code.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

Author: pillo79

scripts/dts/python-devicetree/src/devicetree/dtlib.py

@@ -641,11 +641,16 @@ def __str__(self):
                 elif marker_type is _MarkerType.PHANDLE:
                     s += " &" + ref
                     pos += 4
+                    if pos != len(self.value) and len(s) - array_start > 80:  # noqa: F821
+                        s += array_newline                                    # noqa: F821
+                        array_start = len(s)
                     # Subtle: There might be more data between the phandle and
                     # the next marker, so we can't 'continue' here
                 else:  # marker_type is _MarkerType.UINT*
                     elm_size = _TYPE_TO_N_BYTES[marker_type]
                     s += _N_BYTES_TO_START_STR[elm_size]
+                    array_start = len(s)
+                    array_newline = "\n" + " " * array_start
 
                 while pos != end:
                     num = int.from_bytes(self.value[pos:pos + elm_size],
@@ -656,6 +661,9 @@ def __str__(self):
                         s += f" {hex(num)}"
 
                     pos += elm_size
+                    if pos != len(self.value) and len(s) - array_start > 80:
+                        s += array_newline
+                        array_start = len(s)
 
                 if (pos != 0
                     and (not next_marker

scripts/dts/python-devicetree/tests/test_dtlib.py

@@ -163,6 +163,8 @@ def test_cell_parsing():
 	j = /bits/ 32 < 0x10 0x20 (-1) >;
 	k = /bits/ 64 < 0x10 0x20 (-1) >;
 	l = < 'a' 'b' 'c' >;
+	m = [ 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b ];
+	n = < 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 >;
 };
 """,
 """
@@ -181,6 +183,10 @@ def test_cell_parsing():
 	j = < 0x10 0x20 0xffffffff >;
 	k = /bits/ 64 < 0x10 0x20 0xffffffffffffffff >;
 	l = < 0x61 0x62 0x63 >;
+	m = [ 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A
+	      1B ];
+	n = < 0x0 0x1 0x2 0x3 0x4 0x5 0x6 0x7 0x8 0x9 0xa 0xb 0xc 0xd 0xe 0xf 0x10 0x11 0x12 0x13
+	      0x14 >;
 };
 """)