uboot-imx

rockchip: boot0: align to 0x20 for armv7 '_start'

The '_start' is using as vector table base address, and will write
to VBAR register, so it needs to be aligned to 0x20 for armv7.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
[Updated to current code base:]
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>