Input: st1232 - add support resolution reading

Hard-coding resolution for st1633 device was wrong. Some of LCDs like
YTS700TLBC-02-100C has assembled Sitronix st1633 touchcontroller too. But
the resolution is not 320x480 as was hard-coded.
Add new function which reads correct resolution directly from register.

Signed-off-by: Andrej Valek <andrej.valek@siemens.com>
Link: https://lore.kernel.org/r/20201103073949.12198-1-andrej.valek@siemens.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>