spi/bcm63xx: move register definitions into the driver

Move all register definitions and structs into the driver. This allows
us dropping the platform_data struct and drop any arch specific
includes. Make use of different device names to identify the version of
the block we have.

Since we now have full control over the message width, we can drop the
size check, which was broken anyway, since it never set ret to any error
code.

Also since we now have no arch depedendent resources, we can now allow
compiling it for any arch, hidden behind COMPILE_TEST.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Signed-off-by: Mark Brown <broonie@kernel.org>