Bump tools for fesvr DTM fix

riscv-openocd: mpsse_flush timeout

Check autotools/automake version for OpenOCD build

Hopefully this will cut down on the number of riscv-tools-doesn't-build
questions we get. Sample output:
Starting RISC-V Toolchain build process
OpenOCD build requires at least version 2.74 of autoconf. Aborting.

(Note OpenOCD requires autoconf 2.64, but changed to 2.74 for this
test.)

OpenOCD: Bump to pick up reverted watchpoint behavior

Bump OpenOCD & Debug Tests

Move the README images to doc/

These disappeared from the RISC-V website, so we'll use local versions
now.

Modified README.md for OSX to include libusb as a requirement in brew…