x86/purgatory: Omit use of bin2c

The .incbin assembler directive is much faster than bin2c + $(CC).

Do similar refactoring as in

4c0f032d4963 ("s390/purgatory: Omit use of bin2c").

Please note the .quad directive matches to size_t in C (both 8
byte) because the purgatory is compiled only for the 64-bit kernel.
(KEXEC_FILE depends on X86_64).

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220725020812.622255-2-masahiroy@kernel.org