ARM: i.MX: Use of_clk_get_by_name() for timer clocks for DT case.

ARM: i.MX: Use of_clk_get_by_name() for timer clocks for DT case.

Use of_clk_get_by_name() for timer clocks for DT case.
This patch eliminates a lot of unneeded clk_register_clkdev()
calls for GPT.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>