x86/alternatives: Rename 'struct text_poke_loc' to 'struct smp_text_poke_loc'

Make it clear that this structure is part of the INT3 based
SMP patching facility, not the regular text_poke*() MM-switch
based facility.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Juergen Gross <jgross@suse.com>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250411054105.2341982-19-mingo@kernel.org