ARM: dts: dra7: Separate AM57 dtsi files

AM5 and DRA7 SoC families have different set of modules
in them so the SoC sepecific dtsi files need to be separated.

e.g. Some of the major differences between AM576 and DRA76

		DRA76x	AM576x

USB3		x
USB4		x
ATL		x
VCP		x
MLB		x
ISS		x
PRU-ICSS1		x
PRU-ICSS2		x

This patch only deals with disabling USB3, USB4 and ATL for
AM57 variants.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>