sam3x support.
sam3x: clean up gpio mess.
sam3x: Add some PMC convenience functions.
sam3x: Add USART registers and come convenience functions.
sam3x: Add gpio_init convenience function.
sam3x: Add some pwm convenience funcitons.
sam3x: Correct pmc_xtal_enable to use startup time parameter.
sam3x: Add missing return types to pwm functions.
sam3x: Add convenince functions for setting clocks and usart baudrate.
sam3x: Add usart funciton to enable rx interrupt.
Minor fix to compile functions in rtc.h
lm4f-doc: Sanitize doxygen structure in rcc.h

By somo copypaste error, the doxygen group rcc_defines was defined twice.
Don't do that. Keep Ken's doxygen structure and drop the old one.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Added *.tag files and the new generated sam3x include subdirectory to gitignores.
lm4f: Add UART register definitions

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
lm4f: Add UART "convenience" macros

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
lm4f: Add basic UART implementation

Add basic functionality needed to setup the UART and send/recieve data.
Interrupts, DMA, and more advanced features are not implemented in this patch.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
lm4f: Implement UART interrupt control

Add a complete API for controlling the UART interrupts.
Doxygen documentation with inline code examples is also provided in this patch.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
lm4f: Implement DMA enable/disable functions for the UART

Add basic rx/tx_dma_enable/disable functionality.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Adding basic support for v7m sync primatives and mutex convenience functions.