block/vpc: Pad VHDFooter, replace uint8_t[] buffers

block/vpc: Pad VHDFooter, replace uint8_t[] buffers

Pad VHDFooter as specified in the "Virtual Hard Disk Image Format
Specification" version 1.0[*].  Change footer buffers from
uint8_t[HEADER_SIZE] to VHDFooter.  Their size remains the same.

The VHDFooter * variables pointing to a VHDFooter variable right next
to it are now silly.  Eliminate them, and shorten the remaining
variables' names.

Most variables pointing to s->footer are now also silly.  Eliminate
them, too.

[*] http://download.microsoft.com/download/f/f/e/ffef50a5-07dd-4cf8-aaa3-442c0673a029/Virtual%20Hard%20Disk%20Format%20Spec_10_18_06.doc

Signed-off-by: Markus Armbruster <[email protected]>
Message-Id: <20201217162003.1102738[email protected]>
Reviewed-by: Max Reitz <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>