[ARM] pxa: update {corgi,spitz}_defconfig to favor SPI-based drivers

Recent changes have been made to use the generic SPI-based ads7846
touch screen driver and a generic SPI-based corgi-type LCD/backlight
driver. Update the {corgi,spitz}_defconfig to favor the use of these
drivers instead of the legacy ones.

Signed-off-by: Eric Miao <eric.miao@marvell.com>