spi: bcm63xx-hsspi: add bcm63xx HSSPI driver

Add a driver for the High Speed SPI controller found on newer BCM63XX SoCs.

It does feature some new modes like 3-wire or dual spi, but neither of it
is currently implemented.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Signed-off-by: Mark Brown <broonie@linaro.org>

diff --cc drivers/spi/Kconfig
Simple merge

diff --cc drivers/spi/Makefile
Simple merge

diff --cc drivers/spi/spi-bcm63xx-hsspi.c
Simple merge