ath11k: add support one MSI vector

On some platforms it's not possible to allocate 32 MSI vectors for various
reasons, be it kernel configuration, VT-d disabled, buggy BIOS etc. So
ath11k was not able to use QCA6390 PCI devices on those platforms. Add
support for one MSI vector to solve that.

In case of one MSI vector, interrupt migration needs to be disabled.  This
is because when interrupt migration happens, the msi_data may change.
However, msi_data is already programmed to rings during initial phase and
ath11k has no way to know that msi_data is changed during run time and
reprogram again.

In case of one MSI vector, MHI subsystem should not use IRQF_NO_SUSPEND
as QCA6390 doesn't set this flag too. Ath11k doesn't need to leave
IRQ enabled in suspend state.

Tested-on: QCA6390 hw2.0 PCI WLAN.HST.1.0.1-01740-QCAHSTSWPLZ_V2_TO_X86-1

Signed-off-by: Carl Huang <cjhuang@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Baochen Qiang <bqiang@codeaurora.org>
Link: https://lore.kernel.org/r/20211026041714.5219-1-bqiang@codeaurora.org