PCI: hv: Replace retarget_msi_interrupt_params with hyperv_pcpu_input_arg

PCI: hv: Replace retarget_msi_interrupt_params with hyperv_pcpu_input_arg

4 commits are involved here:
A (2016): commit 0de8ce3ee8e3 ("PCI: hv: Allocate physically contiguous hypercall params buffer")
B (2017): commit be66b6736591 ("PCI: hv: Use page allocation for hbus structure")
C (2019): commit 877b911a5ba0 ("PCI: hv: Avoid a kmemleak false positive caused by the hbus buffer")
D (2018): commit 68bb7bfb7985 ("X86/Hyper-V: Enable IPI enlightenments")

Patch D introduced the per-CPU hypercall input page "hyperv_pcpu_input_arg"
in 2018. With patch D, we no longer need the per-Hyper-V-PCI-bus hypercall
input page "hbus->retarget_msi_interrupt_params" that was added in patch A,
and the issue addressed by patch B is no longer an issue, and we can also
get rid of patch C.

The change here is required for PCI device assignment to work for
Confidential VMs (CVMs) running without a paravisor, because otherwise we
would have to call set_memory_decrypted() for
"hbus->retarget_msi_interrupt_params" before calling the hypercall
HVCALL_RETARGET_INTERRUPT.

Signed-off-by: Dexuan Cui <[email protected]>
Reviewed-by: Michael Kelley <[email protected]>
Acked-by: Lorenzo Pieralisi <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Wei Liu <[email protected]>