riscv: Update Microchip MPFS Icicle Kit support

This patch updates Microchip MPFS Icicle Kit support. For now,
add Microchip QSPI driver and a small 4MB reservation is
made at the end of 32-bit DDR to provide some memory for
the HSS to use.

Signed-off-by: Padmarao Begari <padmarao.begari@microchip.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Rick Chen <rick@andestech.com>