hikey*: Undef BL32_BASE when building without SPD

Otherwise, BL2 tries to load a BL32 image and triggers
assert(result == 0)
in
plat_get_image_source()
in hikey{960}_io_storage.c
in a debug build, or displays
ERROR:   BL2: Failed to load image
in a release build.

Signed-off-by: Victor Chong <victor.chong@linaro.org>
2 files changed