dts: i2s_mcux_sai: Clarify IOMUXC GPR binding

Improve the documentation of the IOMUXC GPR binding so that it is
clear what the cells in the specifier space of "pinmux" space mean. And
change the names of the cells to be more appropriate. "offset" instead
of "pin" and "mask" instead of "function" describes more precisely what
the cells in the specifier mean.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>

Author: decsny

drivers/i2s/i2s_mcux_sai.c

@@ -1153,8 +1153,8 @@ static DEVICE_API(i2s, i2s_mcux_driver_api) = {
 		.pll_num = DT_PHA_BY_NAME_OR(DT_DRV_INST(i2s_id), pll_clocks, num, value, 0),      \
 		.pll_den = DT_PHA_BY_NAME_OR(DT_DRV_INST(i2s_id), pll_clocks, den, value, 0),      \
 		.mclk_control_base = DT_REG_ADDR(DT_PHANDLE(DT_DRV_INST(i2s_id), pinmuxes)),       \
-		.mclk_pin_mask = DT_PHA_BY_IDX(DT_DRV_INST(i2s_id), pinmuxes, 0, function),        \
-		.mclk_pin_offset = DT_PHA_BY_IDX(DT_DRV_INST(i2s_id), pinmuxes, 0, pin),           \
+		.mclk_pin_mask = DT_PHA_BY_IDX(DT_DRV_INST(i2s_id), pinmuxes, 0, mask),            \
+		.mclk_pin_offset = DT_PHA_BY_IDX(DT_DRV_INST(i2s_id), pinmuxes, 0, offset),        \
 		.clk_sub_sys =                                                                     \
 			(clock_control_subsys_t)DT_INST_CLOCKS_CELL_BY_IDX(i2s_id, 0, name),       \
 		.ccm_dev = DEVICE_DT_GET(DT_INST_CLOCKS_CTLR(i2s_id)),                             \

dts/bindings/pinctrl/nxp,imx-gpr.yaml

@@ -1,7 +1,14 @@
 # Copyright (c) 2021, NXP
 # SPDX-License-Identifier: Apache-2.0
 
-description: i.MX IOMUXC node
+description: |
+  i.MX IOMUXC node
+
+  The specifier space "pinmux" of this binding should have two cells describing
+  the resources needed from the GPR registers.
+  For each specifier, the first cell should be the offset of the GPR register in bytes
+  from the base address of the GPR device base address. The second cell should be a
+  bitmask indicating which bits in the specified register are relevant to the referencing device.
 
 compatible: "nxp,imx-gpr"
 
@@ -12,5 +19,5 @@ properties:
     required: true
 
 pinmux-cells:
-  - pin
-  - function
+  - offset
+  - mask