wifi: ath12k: Refactor core startup

In the upcoming hardware device group abstraction radios across different
devices can be grouped together to support multi-link operation and register as
a device group to mac80211.

Currently, ath12k_mac_allocate() and ath12k_mac_register() are part of
ath12k_core_start() and ath12k_core_pdev_create() respectively and are based on
per device (struct ath12k_base). These APIs can be decoupled and moved out to
ath12k_core_qmi_firmware_ready() itself. This refactor is helpful for device
group abstraction when mac80211 allocate and register will be changed from per
device (struct ath12k_base) to per device group (struct ath12k_hw_group).

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.3.1-00173-QCAHKSWPL_SILICONZ-1
Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3

Signed-off-by: Karthikeyan Periyasamy <quic_periyasa@quicinc.com>
Signed-off-by: Harshitha Prem <quic_hprem@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Patchwork-Id: 13888256