OvmfPkg: Fix SevMemoryAcceptance memory attributes

OvmfPkg: Fix SevMemoryAcceptance memory attributes

The hard-coded attributes for the re-added memory space should instead
forward the replaced descriptor's capabilities.

Tested on Linux with efi=debug. Prior to this change, an 8GiB VM running
a kernel without unaccepted memory support shows this entry

efi: mem94: [Conventional|   |  |CC|  |  |  |  |  |  |   |  |  |  |  ]
range=[0x0000000100000000-0x000000023fffffff] (5120MB)

This does not have the cache capabilities one would expect for system
memory, UC|WC|WT|WB.

After this change, the same entry becomes

efi: mem94: [Conventional|   |  |CC|  |  |  |  |  |  |   |WB|WT|WC|UC]
range=[0x0000000100000000-0x000000023fffffff] (5120MB)

This has all the expected attributes.

Cc: Erdem Aktas <erdemaktas@google.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Michael Roth <michael.roth@amd.com>
Signed-off-by: Dionna Glaze <dionnaglaze@google.com>
[ardb: drop the EFI_MEMORY_CPU_CRYPTO flag - it isn't used anywhere else
       in EDK2 or Linux so it doesn't actually do anything, and it is
       unclear whether it is intended for use by the guest in the first
       place]
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>