While on all current chips, exticr gpio port mux selection is coded on 4 bits, stm32g0 EXTI_EXTICR register uses 8 bits. Align all exti header to reference that value (was previously defined for f0 as SYCFG_EXTICR_SKIP)
Modified to update to latest reference manual. Changes to CFGR3, some extra bits. Signed-off-by: Karl Palsson <karlp@tweak.net.au>