Linux to posix conversion

Changed "linux" target to "posix". Most of the changes are shared with
QuRT and with OSX. The Linux specific parts are in for i2c which uses
<linux/i2c.h> and <linux/i2c-dev.h>.

There is also a check for __PX4_LINUX in mavlink for a tty ioctl that is
not supported.

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

src/drivers/rgbled/module.mk

@@ -7,7 +7,7 @@ MODULE_COMMAND	 = rgbled
 ifeq ($(PX4_TARGET_OS),nuttx)
 SRCS		 = rgbled.cpp
 else
-SRCS		 = rgbled_linux.cpp
+SRCS		 = rgbled_posix.cpp
 endif
 
 MAXOPTIMIZATION	 = -Os