package/rwmem: new package

rwmem is small tool to read & write device registers. Some of the
features include:

- support mmaped and i2c devices
- addressing with 8/16/32/64 bit addresses
- accessing 8/16/32/64 bit memory locations
- little and big endian addressess and accesses
- bitfields
- address ranges
- register description database

Python bindings are disabled for now.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>