spi: Add Microchip PolarFire SoC QSPI driver

Add QSPI driver code for the Microchip PolarFire SoC.
This driver supports the QSPI standard, dual and quad
mode interfaces.

Co-developed-by: Naga Sureshkumar Relli <nagasuresh.relli@microchip.com>
Signed-off-by: Naga Sureshkumar Relli <nagasuresh.relli@microchip.com>
Signed-off-by: Padmarao Begari <padmarao.begari@microchip.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>