linux/kernel.h isn't needed by asm/atomic.h and will result in circular
dependencies when the asm-generic atomic bitops are built around the
tomic_long_t interface.

Remove the broad include and replace it with linux/compiler.h for
READ_ONCE etc and asm/irqflags.h for arch_local_irq_save etc.

Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Yoshinori Sato <ysato@users.sourceforge.jp>