arm: mvebu: Use CONFIG_TIMER on all MVEBU & KIRKWOOD platforms

Now that the new timer support is available for these platforms, let's
select this IF for all these platforms. This way it's not necessary
that each board changes it's config header.

Signed-off-by: Stefan Roese <sr@denx.de>
Tested-by: Tony Dinh <mibodhi@gmail.com>