docs: updated qemu-img man page and qemu-doc to reflect VHDX support.

The man page for qemu-img, and the qemu-doc, did not mention VHDX
as a supported format.  This adds in reference to VHDX in those
documents.

[Stefan Weil <sw@weilnetz.de> suggested s/Block Size/Block size/ for
consistency.  I have made this change.
--Stefan]

Signed-off-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

qemu-doc.texi

@@ -654,6 +654,21 @@ Supported options:
 Specifies which VHD subformat to use. Valid options are
 @code{dynamic} (default) and @code{fixed}.
 @end table
+
+@item VHDX
+Hyper-V compatible image format (VHDX).
+Supported options:
+@table @code
+@item subformat
+Specifies which VHDX subformat to use. Valid options are
+@code{dynamic} (default) and @code{fixed}.
+@item block_state_zero
+Force use of payload blocks of type 'ZERO'.
+@item block_size
+Block size; min 1 MB, max 256 MB.  0 means auto-calculate based on image size.
+@item log_size
+Log size; min 1 MB.
+@end table
 @end table
 
 @subsubsection Read-only formats

qemu-img.texi

@@ -431,8 +431,8 @@ This option can only be enabled if @code{compat=1.1} is specified.
 
 @item Other
 QEMU also supports various other image file formats for compatibility with
-older QEMU versions or other hypervisors, including VMDK, VDI, VHD (vpc), qcow1
+older QEMU versions or other hypervisors, including VMDK, VDI, VHD (vpc), VHDX,
-and QED. For a full list of supported formats see @code{qemu-img --help}.
+qcow1 and QED. For a full list of supported formats see @code{qemu-img --help}.
 For a more detailed description of these formats, see the QEMU Emulation User
 Documentation.