efi_loader: Fix link of EFI apps with ld.lld

When compiling U-Boot with ld.lld as the linker, the helloworld EFI app
example fails to link:

LD      lib/efi_loader/helloworld_efi.so
ld.lld: error: section: .dynamic is not contiguous with other relro
                        sections

LLD will always create RELRO program header regardless of target
emulation, whereas BFD may automatically disable it for unsupported
targets. Add -znorelro to disable it explicitly in all cases.

Signed-off-by: Alistair Delva <adelva@google.com>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>