CLK: TI: add DT alias clock registration mechanism

Some devices require their clocks to be available with a specific
dev-id con-id mapping. With DT, the clocks can be found by default
only with their name, or alternatively through the device node of
the consumer. With drivers, that don't support DT fully yet, add
mechanism to register specific clock names.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>