x86/alternatives: fully leverage automatic NOP filling

x86/alternatives: fully leverage automatic NOP filling

As of commit 4008c71d7a ("x86/alt: Support for automatic padding
calculations") there's no point having explict ASM_NOPn instances in
alternatives anymore - drop them. As a result also drop the asm/nops.h
inclusion from alternative.h, adding explicit inclusions in the two
remaining C files needing them.

While touching it also move the CR4_PV32_RESTORE definition out of the
SMAP-specific conditional into a more general one.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>