Axim X50 touchscreen patch

Hi all,

you'll find attached a patch with the following modifications :
- add ADS7846/TSC2046 touchscreen support to Axim X50 (thanks for this
nice job, Paul !)
- small fixes in pxafb.c and aximx50_buttons.c (build warnings)
- tabulation clean up in aximx50.c
- use SSCR0_SerClkDiv in ads7846_adc_ssp.c
- updated aximx50_defconfig

It should apply on the current HEAD kernel.

Of course, your remarks are welcome :-)

Pierre