ARM: mx6: Allow enablement of FEC Anatop based clock for all MX6

The enable_fec_anatop_clock method should be available for all MX6
variant as it is not MX6 SoloLite specific. This moves the code out of
the #ifdef/#endif and we make it conditional to CONFIG_FEC_MXC
instead.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Acked-by: Stefano Babic <sbabic@denx.de>