x86/purgatory: Hard-code obj-y in Makefile

arch/x86/Kbuild guards the entire purgatory/ directory, and
CONFIG_KEXEC_FILE is bool type.

$(CONFIG_KEXEC_FILE) is always 'y' when this directory is being built.

Signed-off-by: Masahiro Yamada <[e-mail]>
Signed-off-by: Borislav Petkov <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/x86/purgatory/Makefile

···
 $(obj)/kexec-purgatory.c: $(obj)/purgatory.ro $(obj)/purgatory.chk FORCE
 	$(call if_changed,bin2c)
 
-obj-$(CONFIG_KEXEC_FILE)	+= kexec-purgatory.o
+obj-y += kexec-purgatory.o