soc: riscv: bouffalolab: 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 Bouffalolab SoC. Therefore, the function is dead code.

Although the implementation is more complex than the default, it results
in the same behavior, making it effectively redundant.

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

Author: miggazElquez

soc/bflb/common/soc_irq.S

@@ -29,30 +29,3 @@ SECTION_FUNC(exception.other, __soc_handle_irq)
 
 	/* Return */
 	jalr x0, ra
-
-/*
- * __soc_is_irq is defined as .weak to allow re-implementation by
- * SOCs that does not truly follow the riscv privilege specification.
- */
-WTEXT(__soc_is_irq)
-
-/*
- * SOC-specific function to determine if the exception is the result of a
- * an interrupt or an exception
- * return 1 (interrupt) or 0 (exception)
- *
- */
-SECTION_FUNC(exception.other, __soc_is_irq)
-	/* Read mcause and check if interrupt bit is set */
-	csrr t0, mcause
-	li t1, SOC_MCAUSE_IRQ_MASK
-	and t0, t0, t1
-
-	/* If interrupt bit is not set, return with 0 */
-	addi a0, x0, 0
-	beqz t0, not_interrupt
-	addi a0, a0, 1
-
-not_interrupt:
-	/* return */
-	jalr x0, ra