wifi: ath12k: Convert ath12k_dp member in ath12k_base to pointer

wifi: ath12k: Convert ath12k_dp member in ath12k_base to pointer

Currently, the Data Path (DP) specific device object (ath12k_dp) is
embedded directly within the ath12k_base structure. The DP object cannot
be extended with architecture-specific fields within a contiguous memory
block with this design.

To address this, convert ath12k_dp into a dynamically allocated object
and store it as a pointer in ath12k_base. This change allows allocation
and initialization of ath12k_dp based on the underlying hardware
architecture. Architecture-specific fields can now be maintained as
private data within a contiguous memory block of ath12k_dp.

This patch (and the forthcoming patches) are intended to serve the purpose
of refactoring different DP objects for the Next Generation ath12k
driver.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.4.1-00199-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: Ripan Deuri <quic_rdeuri@quicinc.com>
Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Reviewed-by: Baochen Qiang <baochen.qiang@oss.qualcomm.com>
Link: https://patch.msgid.link/20250930131005.2884253-2-quic_rdeuri@quicinc.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>