intel-socfpga: dts: improve qspi node for rsu feature

commit d112e704

 from
git://git.yoctoproject.org/linux-yocto v5.10/standard/intel-sdk-5.10/intel-socfpga.

The MTD partition used by LIBRSU must start at the beginning of
SPT0(sub-partition table 0) in flash

Signed-off-by: Meng Li <Meng.Li@windriver.com>
Signed-off-by: Liwei Song <liwei.song@windriver.com>