spi: remove old Cadence xSPI driver

commit e1e7872e028766124e4968220fe6e2993d1d0ed9 from
git@git.assembla.com:cavium/WindRiver.linux.git

Remove old SPI driver

Signed-off-by: Witold Sadowski <wsadowski@marvell.com>
Change-Id: Iaa46d6f7d200e9752b05760801cae6f671872a6d
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/67401
Reviewed-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Tested-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>