[ARM] pxa: make PXA3xx_CK() and PXA3xx_CKEN() public in clock.h

So processor specific clock sources can be defined in pxa300.c
and pxa320.c.

Signed-off-by: eric miao <eric.miao@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>