UniPhier SoC updates for v2020.04 (2nd)

Denali NAND driver changes:
 - Set up more registers in denali-spl for SOCFPGA
 - Make clocks optional
 - Do not assert reset signals in the remove hook
 - associate SPARE_AREA_SKIP_BYTES with DT compatible
 - switch to UCLASS_MTD

UniPhier platform changes:
 - fix a bug in dram_init()
 - specify loadaddr for "source" command