[ARM] 4213/1: S3C2410 - Update definition of ADCTSC_XY_PST

Update S3C2410_ADCTSC_XY_PST macro to allow setting the ADCTSC_XY_PST
bits.

Signed-off-by: Arnaud Patard <arnaud.patard@rtp-net.org>
Acked-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>