bluetooth: hci_nxp: disallow standby usage while sending HCI MSG

Sending an HCI message requires to wake up the controller
core if it's asleep. Platform controllers may send responses using
non wakeable interrupts and those can be lost during standby usage.
Blocking standby usage until the HCI message is sent.

Signed-off-by: Yassine El Aissaoui <yassine.elaissaoui@nxp.com>