Fix fractional seconds (again)

Ok, seriously, why can't I get this right...
Add support for 64MHz and update TI patch data

Add compiler defs to allow for 64MHz modules
Update TI SDK data to v1.24
Fix zero length POST requests and update RNXV serial

Fix handling of POST requests that explicitly set Content-Length to zero.
Fix RN-XV serial to handl disconnected sockets correctly.
Add example testing fro zero length POSTs.
Fix 64MHz mode and add 48MHz mode

This fixes some minor problems with 64MHz mode and add support for
48MHz as well.  This includes fixing using half-cycle flash access
which was never valid but seemed to be ignored.  The RAM and CPU
definitions are also moved entirely to the makefiles.