chip: stm32: Enable additional I2C/UART DMA channels for STM32F412
chip: stm32: Enable additional I2C/UART DMA channels for STM32F412

Enable additional I2C/UART DMA channel mappings for STM32F412 chip
variant. Introduce new CHIP_VARIANT_STM32F41X define, to simplify
further refactoring.

BUG=none
BRANCH=none
TEST=build

Signed-off-by: Moritz Fischer <16c4312f096cb05ec900643fe7a5f22f7761ab4a@ettus.com>
Change-Id: I61ed545619ddda8846e598fcb461cf971fc9b905
Reviewed-on: https://chromium-review.googlesource.com/1404103
Commit-Ready: ChromeOS CL Exonerator Bot <fa429e5907f00867f797423aea74327bb02c91b6@appspot.gserviceaccount.com>
Reviewed-by: Philip Chen <3ee404f9ef892bc3fda6e6a76e65843b5fa44db2@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec