spi: add TI QSPI driver

Adds a SPI master driver for the TI QSPI peripheral.
- Added quad read support.
- Added memory mapped support.

Signed-off-by: Matt Porter <matt.porter@linaro.org>
Signed-off-by: Sourav Poddar <sourav.poddar@ti.com>
Signed-off-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>