Cooja: allow setting RSSI while sending and silence

It is now possible to set the RSSI while the radio is sending or when
no radiodata is received. This is now supported by all radiomediums
exept MRM. This also includes a GUI to configure the values.
CC2538: Add a Makefile rule to generate a final assembly listing.
Fix CC2538 random_init lockup

Contiki sometimes fails to boot correctly and locks up in
random_init()

This problem only manifests itself for specific versions
of the arm-gcc toolchain and then again only for specific
levels of optimisation (-Os vs -O2, depending on the
value of the SMALL make variable)

The lockup is caused when we write an RFCORE XREG before
the RF clock ungating has taken effect, which in turn
only occurs depending on the assembly generated for those
two instructions:

  REG(SYS_CTRL_RCGCRFC) = 1;

  REG(RFCORE_XREG_FRMCTRL0) = 0x00000008;

This commit makes the RNG wait for the ungating to take
effect before attempting to write the register
Add a note about "make cc2538-demo.lst" to the platform README.
cc2538: uart: Make it possible to use several UARTs simultaneously

This avoids the limitation of having a single UART available at runtime, without
duplicating code.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Merge pull request #623 from ADVANSEE/cc2538-multi-uart

cc2538: uart: Make it possible to use several UARTs simultaneously
Merge pull request #616 from hexluthor/listing

CC2538: Add a Makefile rule to generate a final assembly listing.
Merge pull request #636 from g-oikonomou/fix-random-init-lockup

Fix CC2538 random_init lockup
Fix Travis failure

For travis tests, we host pre-built bundles of the arm-gcc and sdcc
toolchains on github, and we download them with curl

Apparently, the URL for those bundles has been changed and the
HTTP response is a 301 redirect. curl doesn't follow it

We change .travis.yml to pull the bundles form the new location
Merge pull request #662 from g-oikonomou/travis-url-fix

Fix Travis failure
Fix exported simulation: add jsyntaxpane JAR, start simulation with maximum speed
Merge pull request #663 from jdede/fix-cooja-export

Fix exported simulation: add jsyntaxpane JAR, start simulation
Merge pull request #450 from darki2002/DGRM_support_BaseRSSI

Base RSSI support for DGRM