brcm63xx: use more systematic names for image and DTS files

This changes brcm63xx target to achieve consistency between image
names, device nodes names, compatible, DTS name and device name
as much as possible. As with other targets, having consistent
names is supposed to make life easier for developers and reduces
the number of "variables" in the system. In particular, applying
the DTS scheme will make it easier to find the correct file and
architecture.

DTS files are named based on the increasingly common
soc-vendor-model scheme, using hyphens for separation as this seems
to be the kernel way. Since the compatible is not used at the
moment, I took the chance to also align them with this patch.

For the SOC, the already existing CFE_CHIP_ID can be exploiting
for all but two devices.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>