lm4f: Add API for enabling/disabling peripherals clock source

The enum definitions are specified in the form
 31:5 register offset from SYSCTL_BASE for the clock register
 4:0  bit offset for the given peripheral

The names have the form [clock_type]_[periph_type]_[periph_number]
Where clock_type is
     RCC for run clock
     SCC for sleep clock
     DCC for deep-sleep clock

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>

lib/lm4f/Makefile

@@ -28,7 +28,7 @@ CFLAGS		= -Os -g -Wall -Wextra -I../../include -fno-common \
 		  -ffunction-sections -fdata-sections -MD -DLM4F
 # ARFLAGS	= rcsv
 ARFLAGS		= rcs
-OBJS		= gpio.o vector.o assert.o
+OBJS		= gpio.o vector.o assert.o systemcontrol.o
 
 VPATH += ../cm3