This patch adds logic to treat virtual ramdisk SPA as pmem region, then
ramdisk's /dev/pmem* device can be mounted with iso9660.

It's useful to work with the httpboot in EFI firmware to pull a remote
ISO file to the local memory region for booting and installation.

Wiki page of UEFI HTTPBoot with OVMF:
	https://en.opensuse.org/UEFI_HTTPBoot_with_OVMF

The ramdisk function in EDK2/OVMF generates a ACPI0012 root device that
it contains empty _STA but without _DSM:

DefinitionBlock ("ssdt2.aml", "SSDT", 2, "INTEL ", "RamDisk ", 0x00001000)
{
    Scope (\_SB)
    {
        Device (NVDR)
        {
            Name (_HID, "ACPI0012")  // _HID: Hardware ID
            Name (_STR, Unicode ("NVDIMM Root Device"))  // _STR: Description String
            Method (_STA, 0, NotSerialized)  // _STA: Status
            {
                Return (0x0F)
            }
        }
    }
}

In section 5.2.25.2 of ACPI 6.1 spec, it mentions that the "SPA Range
Structure Index" of virtual SPA shall be set to zero. That means virtual SPA
will not be associated by any NVDIMM region mapping.

The VCD's SPA Range Structure in NFIT is similar to virtual disk region
as following:

[028h 0040   2]                Subtable Type : 0000 [System Physical Address Range]
[02Ah 0042   2]                       Length : 0038

[02Ch 0044   2]                  Range Index : 0000
[02Eh 0046   2]        Flags (decoded below) : 0000
                   Add/Online Operation Only : 0
                      Proximity Domain Valid : 0
[030h 0048   4]                     Reserved : 00000000
[034h 0052   4]             Proximity Domain : 00000000
[038h 0056  16]           Address Range GUID : 77AB535A-45FC-624B-5560-F7B281D1F96E
[048h 0072   8]           Address Range Base : 00000000B6ABD018
[050h 0080   8]         Address Range Length : 0000000005500000
[058h 0088   8]         Memory Map Attribute : 0000000000000000

The way to not associate a SPA range is to never reference it from a "flush hint",
"interleave", or "control region" table.

After testing on OVMF, pmem driver can support the region that it doesn't
assoicate to any NVDIMM mapping. So, treat VCD like pmem is a idea to get
a pmem block device that it contains iso.

v4:
Instoduce nfit_spa_is_virtual() to check virtual ramdisk SPA and create
pmem region.

v3:
To simplify patch, removed useless VCD region in libnvdimm.

v2:
Removed the code for setting VCD to a read-only region.

Cc: Gary Lin <GLin@suse.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Linda Knippers <linda.knippers@hpe.com>
Signed-off-by: Lee, Chun-Yi <jlee@suse.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>