x86/asm: Remove opencoded uses of altinstruction_entry

x86/asm: Remove opencoded uses of altinstruction_entry

With future changes, altinstruction_entry is going to become more complicated
to use.  Furthermore, there are already ALTERNATIVE* macros which can be used
to avoid opencoding the creation of replacement information.

For ASM_STAC, ASM_CLAC and CR4_PV32_RESTORE, this means the removal of all
hardocded label numbers.  For the cr4_pv32 alternatives, this means hardcoding
the extra space required in the original patch site, but the hardcoding will
be removed by a later patch.

No change to any functionality, but the handling of nops inside the original
patch sites are a bit different.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>