To i.MX6SX/UL, two ethernet interfaces are supported.
Add ENET2 clock support:
1. Introduce a new input parameter "fec_id", only 0 and 1 are allowed.
   To value 1, only i.MX6SX/UL can pass the check.
2. Modify board code who use this api to follow new api prototype.

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Stefan Roese <sr@denx.de>
Cc: Nikolaos Pasaloukos <Nikolaos.Pasaloukos@imgtec.com>
Cc: Stefano Babic <sbabic@denx.de>
Reviewed-by: Stefan Roese <sr@denx.de>