arm: socfpga: arria10: Setting image magic value to romcode initswstate reg

The romcode_initswstate register need to be set with FSBL_IMAGE_IS_VALID
value if the current FSBL image is found valid, otherwise BootROM will
look for next subsequent valid FSBL image when warm reset is triggered.

Signed-off-by: Tien Fong Chee <tien.fong.chee@intel.com>
Signed-off-by: Sin Hui Kho <sin.hui.kho@intel.com>
Reviewed-by: Tien Fong Chee <tien.fong.chee@intel.com>