x86/link: Don't merge .init.text and .init.data

x86/link: Don't merge .init.text and .init.data

c/s 1308f0170c merged .init.text and .init.data, because EFI might properly
write-protect r/o sections.

However, that change makes xen-syms unusable for disassembly analysis.  In
particular, searching for indirect branches as part of the SP2/Spectre
mitigation series.

As the merging isn't necessary for ELF targets at all, make it conditional on
the EFI side of the build.

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