arm: Use WFI instruction for arch_cpu_idle function

According to the ​ARMv7 Reference Manual, "Wait for Interrupt" is supported only through the WFI instruction on ARMv7.
The currently used ARMv6 equivalent may not work on ARMv7 and newer CPUs.

Fixes #18520

Change-Id: I69a136870654be33c0c789004e08bf610db3dd97
Reviewed-on: https://review.haiku-os.org/c/haiku/+/8044
Haiku-Format: Haiku-format Bot <[email protected]>
Reviewed-by: waddlesplash <[email protected]>

headers/private/kernel/arch/arm/arch_cpu.h

@@ -14,6 +14,7 @@
 #define isb() __asm__ __volatile__("isb" : : : "memory")
 #define dsb() __asm__ __volatile__("dsb" : : : "memory")
 #define dmb() __asm__ __volatile__("dmb" : : : "memory")
+#define wfi() __asm__ __volatile__("wfi" : : : "memory")
 
 #define set_ac()
 #define clear_ac()
@@ -122,9 +123,7 @@ arch_cpu_pause(void)
 static inline void
 arch_cpu_idle(void)
 {
-	uint32 Rd = 0;
-	asm volatile("mcr p15, 0, %[c7format], c7, c0, 4"
-		: : [c7format] "r" (Rd) );
+	wfi();
 }