As exception among the i.MX processors, the i.MX31 has headers
without general names (mx31-regs.h, mx31.h instead of imx-regs.h and
clock.h). This requires several nasty #ifdef in the drivers to
include the correct header. The patch cleans up the driver and
renames the header files as for the other i.MX processors.

Signed-off-by: Stefano Babic <sbabic@denx.de>