arm64: Remove unnecessary irqflags alternative.h include

Since commit 20af807d806d ("arm64: Avoid cpus_have_const_cap() for
ARM64_HAS_GIC_PRIO_MASKING"), the alternative.h include is not used,
so remove it.

Fixes: 20af807d806d ("arm64: Avoid cpus_have_const_cap() for ARM64_HAS_GIC_PRIO_MASKING")
Signed-off-by: Jinjie Ruan <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Will Deacon <[e-mail]>

arch/arm64/include/asm/irqflags.h

···
 #ifndef __ASM_IRQFLAGS_H
 #define __ASM_IRQFLAGS_H
 
-#include <asm/alternative.h>
 #include <asm/barrier.h>
 #include <asm/ptrace.h>
 #include <asm/sysreg.h>