ramips: improve i2s drivers

ramips: improve i2s drivers

* remove mt7620-wm8960.c use simple card and DTS to do it
* add old chips support
* add 12Mhz refclk setup. this is hard code. need use clock framework
  rewrite it
* add interrupt error status support for debug. default disable it.
  because it cause to many interrupts
* add setup bclk suport not hard code it
* add 24 bits support for mt7628. not verified
* use regmap api to control registers
* add txdma-req/rxdma-req DTS params for DMA use

Signed-off-by: Michael Lee <igvtee@gmail.com>