lm4f: Add USB register definitions

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
NOTFORMERGE: Pathetic attempt at implememting a USB driver

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
lm4f: Improve USB EP setup and FIFO allocation
lm4f: Reformat some comments on USB driver; add links to resources
lm4f: Fix typos in "huge block" in lm4f_ep_setup()

zyp> https://github.com/mrnuke/libopencm3/commit/1d27a67 <- what's up with that
huge if block? I think you got a few typos in it.
lm4f: Standardize the USB soft connect/disconnect

Make a connect and disconnect function, since this happens in several places,
and we don;t want to duplicate code unnecessarily.
lm4f: Fix minor bug in USB FIFO allocator
lm4f: Do a proper software reset when initializing USB controller
lm4f: Fix pesky warnings in USB driver
lm4f: Don't bailout on lm4f_disconnect()

This has been tested, and it works.
lm4f: USB: Move RX_FIFO_SIZE define out of the way
lm4f: Implement USB STALL/UNSTALL
lm4f: Get rid of bailout() debug helper
lm4f: Remove FIFO defines from USB driver
lm4f: Remove debug probes (printf) from USB driver