hv: vmsi: refine write_vmsi_cfg implementation

1. disable physical MSI before writing the virtual MSI CFG space
2. do the remap_vmsi if the guest wants to enable MSI or update MSI address or data
3. disable INTx and enable MSI after step 2.

The previous Message Control check depends on the guest write MSI Message Control
Register at the offset of Message Control Register. However, the guest could access
this register at the offset of MSI Capability ID register. This patch remove this
constraint. Also, The previous implementation didn't really disable MSI when guest
wanted to disable MSI.

Tracked-On: #3475
Signed-off-by: Li Fei1 <fei1.li@intel.com>

hypervisor/include/dm/vpci.h

@@ -51,6 +51,7 @@ struct msix_table_entry {
 
 /* MSI capability structure */
 struct pci_msi {
+	bool      is_64bit;
 	uint32_t  capoff;
 	uint32_t  caplen;
 };