zephyr: console: Use DT bindings to get shell uart dev on 2.7+
zephyr: console: Use DT bindings to get shell uart dev on 2.7+

In Zephyr 2.7+, CONFIG_UART_SHELL_ON_DEV_NAME is removed in favor of
using the zephyr,shell-uart device chosen by the UART driver.  Since
we choose zephyr,shell-uart on all of our boards, we are clear to make
this change ahead of the v2.7 uprev.

Also see https://github.com/zephyrproject-rtos/zephyr/pull/37902.

BUG=b:198824039
BRANCH=none
TEST=zmake testall
TEST=compile posix-ec with v2.7_rc1

Signed-off-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>
Change-Id: Ic066ce0617fa900ae7c1c96a2cbece0b698764bc
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3142750
Reviewed-by: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>

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