soc: riscv: wch: Remove unused __soc_is_irq function

The __soc_is_irq function is only used when
CONFIG_RISCV_SOC_EXCEPTION_FROM_IRQ is enabled, which is not the case
for any WCH SoC. The implementation is therefore dead code.

Additionally, the implementation matches the default fallback behavior,
so no functional change would occur even if the config were enabled.

Signed-off-by: Miguel Gazquez <miguel.gazquez@bootlin.com>

Author: miggazElquez

soc/wch/ch32v/ch32v00x/soc_irq.S

@@ -8,13 +8,7 @@
 #include <zephyr/toolchain.h>
 
 /* Exports */
-GTEXT(__soc_is_irq)
 GTEXT(__soc_handle_irq)
 
-SECTION_FUNC(exception.other, __soc_is_irq)
-	csrr a0, mcause
-	srli a0, a0, 31
-	ret
-
 SECTION_FUNC(exception.other, __soc_handle_irq)
 	ret

soc/wch/ch32v/qingke_v2a/soc_irq.S

@@ -7,13 +7,7 @@
 #include <zephyr/toolchain.h>
 
 /* Exports */
-GTEXT(__soc_is_irq)
 GTEXT(__soc_handle_irq)
 
-SECTION_FUNC(exception.other, __soc_is_irq)
-	csrr a0, mcause
-	srli a0, a0, 31
-	ret
-
 SECTION_FUNC(exception.other, __soc_handle_irq)
 	ret

soc/wch/ch32v/qingke_v4b/soc_irq.S

@@ -7,13 +7,7 @@
 #include <zephyr/toolchain.h>
 
 /* Exports */
-GTEXT(__soc_is_irq)
 GTEXT(__soc_handle_irq)
 
-SECTION_FUNC(exception.other, __soc_is_irq)
-	csrr a0, mcause
-	srli a0, a0, 31
-	ret
-
 SECTION_FUNC(exception.other, __soc_handle_irq)
 	ret

soc/wch/ch32v/qingke_v4c/soc_irq.S

@@ -7,13 +7,7 @@
 #include <zephyr/toolchain.h>
 
 /* Exports */
-GTEXT(__soc_is_irq)
 GTEXT(__soc_handle_irq)
 
-SECTION_FUNC(exception.other, __soc_is_irq)
-	csrr a0, mcause
-	srli a0, a0, 31
-	ret
-
 SECTION_FUNC(exception.other, __soc_handle_irq)
 	ret

soc/wch/ch32v/qingke_v4f/soc_irq.S

@@ -7,13 +7,7 @@
 #include <zephyr/toolchain.h>
 
 /* Exports */
-GTEXT(__soc_is_irq)
 GTEXT(__soc_handle_irq)
 
-SECTION_FUNC(exception.other, __soc_is_irq)
-	csrr a0, mcause
-	srli a0, a0, 31
-	ret
-
 SECTION_FUNC(exception.other, __soc_handle_irq)
 	ret