board: ls2088ardb: Extend cs4340_get_fw_addr() functionality

LS2088A-RDB supports TFA boot source and has 2 nor banks(default and
altbank) and QSPI as boot source. The corresponding defconfig can only
have one entry defined and therefore, extend cs4340_get_fw_addr()
function to overwrite firmware address which will be later used in
cortina firmware.

Signed-off-by: Kuldeep Singh <kuldeep.singh@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>