overlays: Add spi0-1cs and spi0-2cs

The spi0-1cs overlay allows the SPI0 interface to be run with a single
CS line, which can be useful if GPIOs are in short supply. The no_miso
parameter is for write-only devices that don't need the return channel,
and again is there to free up a GPIO.

spi0-2cs is the new name for spi0-cs (now deprecated with a redirect
to spi0-2cs), but with the addedd no_miso parameter.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>