boards: arm: bl5340_dvk: Remove disabling of QSPI for BL5340 DVS NS

Remove disable of QSPI for BL5340 DVK cpuapp NS build.
The QSPI is not configured as a secure peripheral in the generic
nrf5340 platform support.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>