stand/efi: Pass --no-dynamic-linker to ld.bfd >= 2.34.

ld.bfd in binutils 2.34+ now reports an error in more cases for custom
ldscripts that do not place PHDRs in a LOAD segment. However, EFI
binaries are not dynamic binaries which need PHDRs, so pass
--no-dynamic-linker to disable this check.

Reviewed by: imp, emaste
Differential Revision: https://reviews.freebsd.org/D34124