x86: prepare merger of <asm/alternative_{32,64}.h>

Prepare for merging <asm/alternative_{32,64}.h> by making the 32- and
64-bit versions textually identical.  This involves:

- removing arbitrary header inclusion differences
- reorganizing the 32-bit version slightly to match the 64-bit version
- using <asm/asm.h> to unify the assembly code
- renaming struct paravirt_patch to struct paravirt_patch_site in the
  64-bit version to match the 32-bit version; there are no references
  to struct paravirt_patch elsewhere in the tree.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>