x86/lib/atomic64_386_32: Rename things

Principally, in order to get rid of #define RET in this code to make
place for a new RET, but also to clarify the code, rename a bunch of
things:

  s/UNLOCK/IRQ_RESTORE/
  s/LOCK/IRQ_SAVE/
  s/BEGIN/BEGIN_IRQ_SAVE/
  s/\<RET\>/RET_IRQ_RESTORE/
  s/RET_ENDP/\tRET_IRQ_RESTORE\rENDP/

which then leaves RET unused so it can be removed.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20211204134907.841623970@infradead.org