Revert "Revert "BACKPORT: efi/libstub/arm64: Set -fpie when building the EFI stub""

In isolation, the original change will break building efistub for ARM64
with gcc.  This wasn't an issue upstream due to the earlier change
60f38de7a8d4 ("efi/libstub: Unify command line param parsing").  That's
now been backported to AOSP too.

This reverts commit 36733457.

Change-Id: I99592a19c77821df897bba966b5486cb835745f9
Signed-off-by: Greg Hackmann <ghackmann@google.com>