x86/kexec: Add the ACPI NVS region to the ident map

With the recent addition of RSDP parsing in the decompression stage,
a kexec-ed kernel now needs ACPI tables to be covered by the identity
mapping. And in commit

  6bbeb276 ("x86/kexec: Add the EFI system tables and ACPI tables to the ident map")

the ACPI tables memory region was added to the ident map.

But some machines have only an ACPI NVS memory region and the ACPI
tables are located in that region. In such case, the kexec-ed kernel
will still fail when trying to access ACPI tables if they're not mapped.

So add the NVS memory region to the ident map as well.

 [ bp: Massage. ]

Fixes: 6bbeb276

 ("x86/kexec: Add the EFI system tables and ACPI tables to the ident map")
Suggested-by: Junichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Kairui Song <kasong@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Junichi Nomura <j-nomura@ce.jp.nec.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Chao Fan <fanc.fnst@cn.fujitsu.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: kexec@lists.infradead.org
Cc: Lianbo Jiang <lijiang@redhat.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190610073617.19767-1-kasong@redhat.com