k64: Change the default serial driver to the mcux one

Stop using the specific uart_k20 driver by default and start using the
more generic mcux uart driver instead.

Jira: ZEP-719
Change-Id: I7b107ea7118887591362159283ebb5413b45595a
Signed-off-by: Maureen Helm <maureen.helm@nxp.com>
3 files changed