x300: Clarified FPGA compat error message
b200: serialized access to get_rx/tx_stream
Merge branch 'maint'

Conflicts:
	host/lib/usrp/b200/b200_impl.hpp
uhd: replaced the `images_error` with a generic utility error

- Deleted images.*, moved functionality to paths.*
- Applies for all devices that check FPGA or FW compat numbers
- Adds generic utility search tool