x86emul: avoid speculative out of bounds accesses

x86emul: avoid speculative out of bounds accesses

There are a few array accesses here the indexes of which are (at least
indirectly) driven by the guest. Use array_access_nospec() to bound
such accesses. In the {,_}decode_gpr() cases replace existing guarding
constructs.

To deal with an otherwise occurring #include cycle, drop the inclusion
of asm/x86_emulate.h from asm/processor.h. This include had been
introduced for obtaining the struct cpuid_leaf declaration, which has
since moved into the x86 helper library.

This is part of the speculative hardening effort.

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