Current imx7d-sdb.dts has some incorrect settings about
Rev-A and Rev-B boards, some of the settings are based on
Rev-A board but some are based on Rev-B board, clean up it
by adding i.MX7D SDB Rev-A board support, make default
imx7d-sdb.dts for Rev-B board as usual, and introduce
imx7d-sdb-reva.dts for Rev-A board. Below are the affected
differences of Rev-A and Rev-B board: