wifi: nrf_wifi: extract `NRF70_SYSTEM_WITH_RAW_MODES`

`NRF70_SYSTEM_WITH_RAW_MODES` is more accurately described as an
additional option on top of `NRF70_SYSTEM_MODE`, not as a unique
choice of `NRF70_OPER_MODES`.

This allows the elimination of multiple `NRF70_SYSTEM_MODE ||
NRF70_SYSTEM_WITH_RAW_MODES` dependencies.

Signed-off-by: Jordan Yates <jordan@embeint.com>