ARM: dts: dra7: workaround UART module disable errata

Add "ti,dra742-uart" to the compatible list so the driver
workaround for UART module disable errata is enabled.

This does not break backward compatibility as existing DTBs
should continue to work with newer kernels albeit without the
capability to idle the UART module when DMA is used.

Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>