MAINTAINERS: ARM/WPCM450: Add 'W:' line with wiki

The wiki is a useful source of 3rd-party information about the SoC,
mostly hardware documentation.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Link: https://lore.kernel.org/r/20220218160834.320200-1-j.neuschaefer@gmx.net


Signed-off-by: Joel Stanley <joel@jms.id.au>