tools: kwbimage: Enforce 128-bit boundary alignment only for Sheeva CPU

This alignment is required only for platforms based on Sheeva CPU core
which are A370 and AXP. Now when U-Boot build system correctly propagates
LOAD_ADDRESS there is no need to have enabled 128-bit boundary alignment on
platforms which do not need it. Previously it was required because load
address was implicitly rounded to 128-bit boundary and U-Boot build system
expected it and misused it. Now with explicit setting of LOAD_ADDRESS there
is no guessing for load address anymore.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>