drivers: nrf_qspi_nor: Exit DPD at driver initialization

It may happen that after the flash chip was previously put into
the Deep Power Down mode, the system was reset but the flash chip
was not. Consequently, the flash chip can be in the DPD mode when
the QSPI driver is initialized. Some flash chips will just exit
the DPD mode on the first CS pulse, but some need to receive the
dedicated command to do it and they will not respond to any other
commands including those that the driver need to perform to complete
its initialization ("Read status register" and "Read JEDEC ID").
This commit adds sending of the "Release from Deep Power Down"
command right after initialization of the QSPI interface to avoid
the problem described above.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>