x86/setup: correct register clobbers for the asm statement when resyncing the stack

x86/setup: correct register clobbers for the asm statement when resyncing the stack

When resyncing the stack, the asm statement does not identify %rsi, %rdi and
%rcx as clobbered by the 'rep movsq'.

Luckily, there are no functional problems in the generated code.  GCC decides
not to save any of them before calling boostrap_map(), which clobbers them.

Correct the clobbers, by listing them as earlyclobber discarded outputs.

Reported-by: Daniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Tested-by: Daniel Kiper <daniel.kiper@oracle.com>