Permit arm32-stub.c to access efi_low_alloc_above() in a subsequent
patch by giving it external linkage and declaring it in efistub.h.
Reviewed-by: NMaxim Uvarov <maxim.uvarov@linaro.org>
Tested-by: NMaxim Uvarov <maxim.uvarov@linaro.org>
Signed-off-by: NArd Biesheuvel <ardb@kernel.org>