arm: dts: bcm283x: Allow UARTs to work before relocation

arm: dts: bcm283x: Allow UARTs to work before relocation

At present the pinctrl nodes are not enabled in pre-relocation U-Boot so
the UARTs do not correctly select the pinconfig to enable the UART pins.
Fix this so that the U-Boot banner is printed.

This fixes serial output on rpi_3b_32b with the following config.txt
options:

   enable_uart=1
   gpu_freq=250

Signed-off-by: Simon Glass <sjg@chromium.org>
Fixes: 9821636b64 (bcm2835_pinctrl: Probe pre-reloc)
Signed-off-by: Matthias Brugger <mbrugger@suse.com>