PCI: dwc: Rename dw_pcie_rp::has_msi_ctrl to dw_pcie_rp::use_imsi_rx for clarity

PCI: dwc: Rename dw_pcie_rp::has_msi_ctrl to dw_pcie_rp::use_imsi_rx for clarity

The current "has_msi_ctrl" flag name is misleading because it suggests the
presence of any MSI controller, while it is specifically set for platforms
that lack .msi_init() callback and don't have "msi-parent" or "msi-map"
device tree properties, indicating they rely on the iMSI-RX module for MSI
functionality.

Rename it to "use_imsi_rx" to make the intent clear:
- When true: Platform uses the iMSI-RX module for MSI handling
- When false: Platform has other MSI controller support (ITS/MBI, external
MSI controller)

No functional changes, only improves code readability and eliminates
naming confusion.

Signed-off-by: Qiang Yu <qiang.yu@oss.qualcomm.com>
[mani: renamed 'uses_imsi_rx' to 'use_imsi_rx' per https://lore.kernel.org/linux-pci/09f9acc1-d1ad-4971-8488-f0268cf08799@rock-chips.com]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Link: https://patch.msgid.link/20260121-remove_cap_clean_up-v1-2-e78115e5d467@oss.qualcomm.com