arm: socfpga: Convert reset manager from struct to defines

Convert reset manager for Gen5, Arria 10 and Stratix 10 from struct
to defines.

Change to get reset manager base address from DT node instead of using
#define.

spl_early_init() initializes the DT setup. So, move spl_early_init() to
beginning of function and before get base address from DT.

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>
Reviewed-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>