fs/proc/vmcore: Enable dumping of encrypted memory when SEV was active

In the kdump kernel, the memory of the first kernel gets to be dumped
into a vmcore file.

Similarly to SME kdump, if SEV was enabled in the first kernel, the old
memory has to be remapped encrypted in order to access it properly.

Commit

  992b649a ("kdump, proc/vmcore: Enable kdumping encrypted memory with SME enabled")

took care of the SME case but it uses sme_active() which checks for SME
only. Use mem_encrypt_active() instead, which returns true when either
SME or SEV is active.

Unlike SME, the second kernel images (kernel and initrd) are loaded into
encrypted memory when SEV is active, hence the kernel elf header must be
remapped as encrypted in order to access it properly.

 [ bp: Massage commit message. ]

Co-developed-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Lianbo Jiang <lijiang@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: bhe@redhat.com
Cc: dyoung@redhat.com
Cc: Ganesh Goudar <ganeshgr@chelsio.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: kexec@lists.infradead.org
Cc: linux-fsdevel@vger.kernel.org
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: mingo@redhat.com
Cc: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Cc: Souptick Joarder <jrdr.linux@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190430074421.7852-4-lijiang@redhat.com