dt-bindings: brcm: rationalize Broadcom documentation naming

This patchset attempts to standardize the naming of dt-bindings
documents based on the Broadcom vendor prefix of brcm.

Although there are no guidelines currently present for how to name
the dt-bindings document the "vendor,binding.txt" style is in use by
some of the other vendors.
Acked-by: NLee Jones <lee@kernel.org>
Acked-by: NFlorian Fainelli <f.fainelli@gmail.com>
Acked-by: NGregory Fong <gregory.0xf0@gmail.com>
Acked-by: NStephen Warren <swarren@wwwdotorg.org>
Signed-off-by: NScott Branden <sbranden@broadcom.com>
Signed-off-by: NRob Herring <robh@kernel.org>