ARM: clk-imx6q: refine clock tree for ESAI

There are three clock for ESAI, esai_extal, esai_ipg, esai_mem. Rename
'esai' to 'esai_extal', 'esai_ahb' to 'esai_mem', and add 'esai_ipg'.
Make the clock for ESAI more clear and align them with imx6sx.

Signed-off-by: Shengjiu Wang <shengjiu.wang@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>