Portions of rcc_clk_enable(), rcc_reset_dev(), and rcc_set_prescaler()
are portable; break these into static inline helpers in
rcc_private.h. These guts of these are portable, but the arrays of
registers etc. are not.
Also add an extern declaration for rcc_dev_table into
rcc_private.h. This lets us put rcc_dev_clk() into a newly resurrected
libmaple/rcc.c, since that's portable.
Signed-off-by: Marti Bolivar <mbolivar@leaflabs.com>
