Revert "arm64: Use aarch64elf and aarch64elfb emulation mode variants"

This reverts commit 38fc4248.

Distributions such as Fedora and Debian do not package the ELF linker
scripts with their toolchains, resulting in kernel build failures such
as:

  |   CHK     include/generated/compile.h
  |   LD [M]  arch/arm64/crypto/sha512-ce.o
  | aarch64-linux-gnu-ld: cannot open linker script file ldscripts/aarch64elf.xr: No such file or directory
  | make[1]: *** [scripts/Makefile.build:530: arch/arm64/crypto/sha512-ce.o] Error 1
  | make: *** [Makefile:1029: arch/arm64/crypto] Error 2

Revert back to the linux targets for now, adding a comment to the Makefile
so we don't accidentally break this in the future.

Cc: Paul Kocialkowski <contact@paulk.fr>
Cc: <stable@vger.kernel.org>
Fixes: 38fc4248

 ("arm64: Use aarch64elf and aarch64elfb emulation mode variants")
Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>