POSIX and QuRT: fixed calls needing px4_ prefix

There were some missed calls to open and ioctl that need to be
px4_open and px4_ioctl.

QuRT also does not provide usleep() so px4_time.h has to be included
in files calling usleep.

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

makefiles/toolchain_hexagon.mk

@@ -90,6 +90,7 @@ ARCHDEFINES		+= -DCONFIG_ARCH_BOARD_$(CONFIG_BOARD) \
 			    -I$(PX4_BASE)/src/platforms/qurt/include \
 			    -I$(PX4_BASE)/../dspal/include \
 			    -I$(PX4_BASE)/../dspal/sys \
+			    -I$(PX4_BASE)/mavlink/include/mavlink \
 			    -Wno-error=shadow
 
 # optimisation flags