[ARM] pxa: make more SSCR0 bit definitions visible on multiple processors

The only exclusive definitions are SSCR0_SCR and SSCR0_SerClkDiv(), loosen
that exclusive #ifdef .. #else .. #endif to allow other definitions to be
visible when slected multiple processors. This helps to pass the building
of pxa-ssp.c.

Signed-off-by: Eric Miao <eric.miao@marvell.com>