Transceiver52M: Separate architecture specific files

Move x86 specific files into their own directory as this
area is about to get crowded with the addition of ARM
support.

Signed-off-by: Thomas Tsou <tom@tsou.cc>
build: Set UHD driver as default configuration

Currently the default configuration is to not build the full
transceiver, which is pointless. Set the UHD driver, which
includes either Ettus or Fairwaves variants, as the default.

Signed-off-by: Thomas Tsou <tom@tsou.cc>