In preparation for allowing architectures to define their own
implementation of the READ_ONCE() macro, move the generic
{READ,WRITE}_ONCE() definitions out of the unwieldy 'linux/compiler.h'
file and into a new 'rwonce.h' header under 'asm-generic'.
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: NPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: NWill Deacon <will@kernel.org>