arm: am57xx: cl-som-am57x: fix USB scan

arm: am57xx: cl-som-am57x: fix USB scan

USB bus scan attempt:
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=> usb start
starting USB...
USB0:   Register 2000140 NbrPorts 2
Starting the controller
USB XHCI 1.00
scanning bus 0 for devices... data abort
pc : [<fff6240e>]          lr : [<fff623b3>]
reloc pc : [<8081b40e>]    lr : [<8081b3b3>]
sp : fdf42930  ip : fdf42960     fp : 00000000
r10: 00000001  r9 : fdf42ef0     r8 : 48890020
r7 : 00000002  r6 : fffa5840     r5 : fff8b140  r4 : fdf429c0
r3 : 00000000  r2 : 00000004     r1 : 00000000  r0 : 00000000
Flags: nZcv  IRQs off  FIQs off  Mode SVC_32
Resetting CPU ...

resetting ...
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Fix by enabling USB configuration in the SPL.

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