x86/alt: Drop explicit padding of origin sites

x86/alt: Drop explicit padding of origin sites

Now that the alternatives infrastructure can calculate the required padding
automatically, there is no need to hard code it.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>