More URL fixes from @peppermint

in my opinion https://px4.io and https://discuss.px4.io is not a working webpage
http://px4.io and http://discuss.px4.io are working

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

Added dspal_math.h

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

Added missing functions that were added for other targets but not for qurt.

Added workaround for missing sem_timedwait(). This may have a performance
impact until a sem_timedwait is supported.

std::to_string is not supported by the hexagon compiler

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

updated ecl ekf2

The mavlink stream from the simulator and the mavlink stream over serial
(used for RC input) both had the same MAVLINK_COMM channel and were
therefore sharing an internal buffer in mavlink_parse_char. This meant
that most (low rate) serial messages were getting swallowed by the high
rate simulator stream.

This change fixes the issue where RC input was not properly arriving in
Gazebo, however it breaks the `commander takeoff` command in SITL which
needs to be investigated.

Fmu pwm limit

MAVLink app: Enable network and serial on POSIX

VTOL fixes for SITL