Bluetooth: hci: spi: use level triggered interrupts

Use level triggered interrupts instead of edge triggered interrupts to
make it impossible for the interrupt line to be active without the RX
thread attempting to read pending data.

This fixes a race condition for re-enabling the interrupt in edge
triggered mode, where `gpio_pin_interrupt_configure_dt` is not called
before the controller re-asserts the interrupt line.

As a result the controller can be reset before booting the RX thread.

Fixes #53980.

Signed-off-by: Jordan Yates <jordan.yates@data61.csiro.au>