mgmt: ec_host_cmd: npcx: workaround for backend SHI

There is an issue on the SHI hardware peripheral to detect CS
rising/failing with bits CSnFE/CSnRE in the EVSTAT2 register in
npcx9m7fb chip. This commit workarounds it by using MIWU to detect the
CS rising and failing.

Signed-off-by: Tom Chang <CHChang19@nuvoton.com>
Signed-off-by: Jun Lin <CHLin56@nuvoton.com>
(cherry picked from commit 07261987)