board_r: Move early-timer init later

At present the early timer init happens as soon as driver model is set up.
This makes it impossible to do anything that needs driver model but must
run before devices are probed (as needed with Intel's FSP-S, for example).

In any case it is not a good idea to tie probing of particular drivers too
closely to the DM init.

Create a new function to init the timer and put it a bit later in the
sequence.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>