Allow placing image to align its entry point with a particular entry
point address. This is needed for SoC's like i.MX8M where
vendor-provided ARM Trusted Firmware blob will exit at specific
pre-determined address and we need to be able to pick execution up
from there.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>