mx25: Define default SoC input clock frequencies

mx25: Define default SoC input clock frequencies

Define default SoC input clock frequencies for i.MX25 in order to get rid of
duplicated definitions.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Matthias Weisser <weisserm@arcor.de>