[lm4f] Remove usb cdc definitions moved to library

Requires a library bump to match
Bump examples library code to get new adc core
Some examples for the STM32F4-Disco board
The SPI-MEMS example, its not great but it does use the SPI
port and can tell you the temperature of the room you are in.
Pulling in some of the makefile changes that are in master into this
branch to make merging easier later on.
Merge branch 'stm32f429-examples' of github.com:ChuckM/libopencm3-examples into stm32f429-examples
Updated to use the new rcc_periph_clock_enable code