spi: bcm-qspi: Add BSPI spi-nor flash controller driver

This change implements BSPI driver for Broadcom BRCMSTB, NS2,
NSP SoCs works in combination with the MSPI controller driver
and implements flash read acceleration and implements  the
spi_flash_read() method. Both MSPI and BSPI controllers are
needed to access spi-nor flash.

Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com>
Signed-off-by: Yendapally Reddy Dhananjaya Reddy <yendapally.reddy@broadcom.com>
Signed-off-by: Mark Brown <broonie@kernel.org>