x86/svm: Clean up construct_vmcb()

x86/svm: Clean up construct_vmcb()

The vmcb is zeroed on allocate - drop all explicit writes of 0.  Move
hvm_update_guest_efer() to co-locate it with the other control register
updates.

Move the BUILD_BUG_ON() into build_assertions(), and add some offset checks
for fields after the large blocks of reserved fields (as these are the most
likely to trigger from a mis-edit).  Take the opportunity to fold 6 adjacent
res* fields into one.

Finally, drop all trailing whitespace in the file.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>