When device runtime pm is enabled on console device, do not suspend
device synchronously on each char transmission, but rather use asynchronous
suspension request.
This will save useless and costly suspension/resumption procedure, which
can involve uart device clock suspension but also pin configuration
to sleep state (which itself involves gpio clock activation ...).
On STM32, using asynch device suspension allows to divide by 3 the
transmission time of a character chain.
Signed-off-by: Erwan Gouriou <erwan.gouriou@st.com>
b98c7942ca