arm: socfpga: arria10: Add save_boot_params()

Add save_boot_params() to save reset status value from bootrom.

Bootrom will clear the status register in reset manager and stores the
reset status value in shared memory. Bootrom stores shared data at last
2KB of onchip RAM.

This function save reset status provided by bootrom to rst_mgr_status.
More information about reset status register value can be found in reset
manager register description.

When running in debugger without bootrom, r0 to r3 are random values.
So, skip save the value when r0 is not bootrom shared data address.

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>