x86, paravirt: Replace GET_CR2_INTO_RCX with GET_CR2_INTO_RAX

x86, paravirt: Replace GET_CR2_INTO_RCX with GET_CR2_INTO_RAX

GET_CR2_INTO_RCX is asinine: it is only used in one place, the actual
paravirt call returns the value in %rax, not %rcx; and the one place
that wants it wants the result in %r9.  We actually generate as a
result of this call:

       call ...
       movq %rax, %rcx
       xorq %rax, %rax		/* this value isn't even used... */
       movq %rcx, %r9

At least make the macro do what the paravirt call does, which is put
the value into %rax.

Nevermind the fact that the macro clobbers all the volatile registers.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Link: http://lkml.kernel.org/r/1334794610-5546-4-git-send-email-hpa@zytor.com
Cc: Glauber de Oliveira Costa <glommer@parallels.com>