boards: up_squared_adsp: provide start address for bootloader

Commit 9987c2e2f99b279a9949ac2419f24f6162ac2e0a spills SoC configs
into architecture files which is less desirable. This provides
the jump address for bootloader, and modifies the bootloader to
jump to __start defined in reset-vector.S. This prepares for
that commit to be reverted.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>
3 files changed