ARM: brcmstb: Add appropriate ARM_BE8() macros for swapping

Building a big-endian kernel for ARCH_BRCMSTB revealed that we would not
be correctly polling for the right bit in the busyuart macro, turns out
there are a few transformations needed to work with big-endian kernels.
First we need to swap the value we read from SUN_TOP_CTRL to properly
compare it against our local tables. Then, just like 8250.S we need to
swap the value before storing it, and conversely swap it after a load.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>