[ARM] 3888/1: add pxa27x SSP FSRT register bit definition

This patch adds a register bit definition for the pxa27x SSP port Frame
Sync Relative Timing (FSRT) bit.

Signed-off-by: Liam Girdwood <liam.girdwood@wolfsonmicro.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>