MX53: add function to set SATA clock to internal

The MX53 SATA interface can use an internal clock (USB PHY1)
instead of an external clock. This is an undocumented feature, but used
on most Freescale's evaluation boards, such as MX53-loco.

As stated by Freescale's support:

Fuses (but not pins) may be used to configure SATA clocks.
Particularly the i.MX53 Fuse_Map contains the next information
about configuring SATA clocks :
	SATA_ALT_REF_CLK[1:0] (offset 0x180C)

'00' - 100MHz (External)
'01' - 50MHz (External)
'10' - 120MHz, internal (USB PHY)
'11' - Reserved

Signed-off-by: Stefano Babic <sbabic@denx.de>
CC: Fabio Estevam <fabio.estevam@freescale.com>