2703/1: pxa-regs.h: complete I2S GPIO alternate functions for PXA27x

Patch from Giorgio Padrin

The patch completes I2S GPIO alternate functions for PXA27x, adding I2S_SYSCLK.
File: pxa-regs.h .

Signed-off-by: Giorgio Padrin
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>