staging: fbtft: Deduplicate driver registration macros

staging: fbtft: Deduplicate driver registration macros

The two macros FBTFT_REGISTER_DRIVER and FBTFT_REGISTER_SPI_DRIVER
contain quite some duplication: Both define an spi driver and an of device
table and the differences are quite subtle.

So create two new macros and use both twice.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20220118181338.207943-2-u.kleine-koenig@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>