Add the register definitions and some of the most basic helper functions
for the new style BCD RTC module found on the F2, F4, L1, F3 and F0.
This tries to keep as close to HACKING_COMMON_DOC as possible, while
maintaining sane names.
All #includes now explicitly use the "<libopencm3/stm32/rcc.h>" format.
If you want to get rid of the "libopencm3" prefix in your local project you
can add a respective -I entry in your Makefile (not recommended though).
All .ld files and .a libs are installed in $(TOOLCHAIN_DIR)/lib
directly (as before), but are now renamed to avoid potential
conflicts now or in the future. Examples:
libopencm3_lpc13xx.a
libopencm3_lpc13xx.ld
libopencm3_stm32.a
libopencm3_stm32.ld
