arm: am57xx: cl-som-am57x: fix Ethernet

arm: am57xx: cl-som-am57x: fix Ethernet

The module is continuously rebooting with the following message:
Net:   data abort
pc : [<fff77f42>]          lr : [<fff6e32b>]
reloc pc : [<80816f42>]    lr : [<8080d32b>]
sp : fdf5ce48  ip : fdf5d79c     fp : 00000017
r10: 8083cd58  r9 : fdf5cef0     r8 : fdf5d5d0
r7 : 48485000  r6 : 400000ff     r5 : fdf5d6e0  r4 : fdf5d618
r3 : fdf5d5b4  r2 : fdf5d5d0     r1 : 643a3631  r0 : fdf5d6e0
Flags: nzCv  IRQs off  FIQs off  Mode SVC_32
Resetting CPU ...

Modifications:
* Enable Ethernet configuration in the SPL.
* Update PINMUX of PHY enable GPIO.

Signed-off-by: Uri Mashiach <uri.mashiach@compulab.co.il>
Reviewed-by: Tom Rini <trini@konsulko.com>