OvmfPkg/VirtioLib: add VirtioMapAllBytesInSharedBuffer() helper function

OvmfPkg/VirtioLib: add VirtioMapAllBytesInSharedBuffer() helper function

The function can be used for mapping the system physical address to virtio
device address using VIRTIO_DEVICE_PROTOCOL.MapSharedBuffer (). The
function helps with centralizing error handling, and it allows the caller
to pass in constant or other evaluated expressions for NumberOfBytes.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
[lersek@redhat.com: s/This/VirtIo/ in the new function's comment blocks]
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>