arm64: Add missing GD_FLG_SKIP_RELOC handling

In case U-Boot enters relocation with GD_FLG_SKIP_RELOC, skip the
relocation. The code still has to set up new_gd pointer and new
stack pointer.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>