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: Lee Jones <lee@kernel.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Gregory Fong <gregory.0xf0@gmail.com>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Scott Branden <sbranden@broadcom.com>
Signed-off-by: Rob Herring <robh@kernel.org>