ARC: don't align ROM region end if not required

This extra MPU alignment of RAMABLE_REGION is only required
if we put ROMABLE_REGION and RAMABLE_REGION into the same
(continuous) memory (i.e. SRAM) - so we won't get beginning of the
RAMABLE_REGION in the end of ROMABLE_REGION MPU aperture.

If we use different regions (ICCM & DCCM, FLASH & SRAM, etc...)
we don't need this extra MPU alignment.

Let's drop it to decrease ROM memory usage.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Evgeniy Paltsev <PaltsevEvgeniy@gmail.com>