ARM: dts: bcm283x: Correct vchiq compatible string

To allow VCHIQ to determine the correct cache line size, use the new
"brcm,bcm2836-vchiq" compatible string on BCM2836 and BCM2837.

Signed-off-by: Phil Elwell <phil@raspberrypi.org>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>