ARM: dts: i.MX25: add the clocks for the EPIT blocks

The i.MX25 contains two EPIT (Enhanced Periodic Interrupt Timer)
function blocks. Add their ipg and per clocks to the device tree.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Acked-by: Clément Péron <peron.clem@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>