stm32g4: Set uart frequency and enable clocks for stm32g4
stm32g4: Set uart frequency and enable clocks for stm32g4

This CL adds changes to enable clocks and configure the uart speed for
stm32g4 chip family.

BUG=b:148493929
BRANCH=None
TEST=verfied that the GPIO, clocks, and EC console over LPUART

Signed-off-by: Scott Collyer <7d40b3eb9e17bf55d972074a5e77a7ea4159f9dd@google.com>
Change-Id: I5600ed64867192fe77fd85fc3dbc0a63f912d738
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2195550
Tested-by: Scott Collyer <7d40b3eb9e17bf55d972074a5e77a7ea4159f9dd@chromium.org>
Reviewed-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>
Commit-Queue: Scott Collyer <7d40b3eb9e17bf55d972074a5e77a7ea4159f9dd@chromium.org>

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