ARM: OMAP4: Add timer clock aliases for device-tree

For OMAP4, the dmtimers are located in the Wake-up, ABE and Peripheral (PER)
power domains. Hence, when the dmtimer is configured to use the "timer_sys_ck"
as its functional clock the actual clock used is different depending on whether
the clock is in the Wake-up, ABE or PER domain. So when we look-up the dmtimer's
"timer_sys_ck" we need to specify the timer device name as well as clock alias
to find the right clock.

Currently, the device names for the timers have the format "omap_timer.X" where
X is the timer instance number. When using to device tree, the format of the
device name created by device-tree is different and has the format
"<reg-address>.<device-name>" (this is assuming that the device-tree "reg"
property is specified). This causes the look-up for the OMAP4 "timer_sys_ck" to
fail. To fix this add new timer clock alias for using device-tree.

Please note that adding a 2nd set of clock aliases for the same clocks to only
temporary until device-tree migration is complete. Then we can remove the legacy
aliases. Hence, I have marked the legacy aliases with a "TODO" to remove them.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
[paul@pwsan.com: updated to apply]
Signed-off-by: Paul Walmsley <paul@pwsan.com>