staging: wilc1000: updated DT binding documentation

staging: wilc1000: updated DT binding documentation

Merged the DT binding documentation of SDIO and SPI into a single file.
Removed documentation for some of the properties which are not required
and handled review comments received in [1] & [2].

[1]. https://lore.kernel.org/linux-wireless/20200303020230.GA15543@bogus
[2]. https://lore.kernel.org/linux-wireless/20200303015558.GA6876@bogus

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Link: https://lore.kernel.org/r/20200307085523.7320-4-ajay.kathat@microchip.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>