drivers: modem: quectel-bg9x: fix reset BG95 mdm

In case of BG95 where there is no reset pin, reseting the board
which uses a BG95 modem could result in powering-off the modem
(as oposed to "reset" the modem). This commit is an attempt
to handle this case and re-power the modem.

Signed-off-by: Andrei Hutanu <andrei.hutanu.i@gmail.com>