i2c: brcmstb: Allow to compile it on BCM2835

The BCM2711, supported by ARCH_BCM2835, also has a controller by the
brcmstb driver so let's allow it to be compiled on that platform.

Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>