x86/EFI: avoid use of GNU ld's --disable-reloc-section when possible

x86/EFI: avoid use of GNU ld's --disable-reloc-section when possible

As of commit 6fa7408d72b3 ("ld: don't generate base relocations in PE
output for absolute symbols") I'm feeling sufficiently confident in GNU
ld to use its logic for generating base relocations, which was enabled
for executables at some point last year (prior to that this would have
got done only for DLLs).

GNU ld, seeing the original relocations coming from the ELF object files,
generates different relocation types for our page tables (64-bit ones,
while mkreloc produces 32-bit ones). This requires also permitting and
handling that type in efi_arch_relocate_image().

Note that in the case that we leave base relocation generation to ld,
while efi/relocs-dummy.o then won't be linked into any executable
anymore, it still needs generating (and hence dependencies need to be
kept as they are) in order to have VIRT_BASE pulled out of it.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>