x86/hvm: unify stdvga mmio intercept with standard mmio intercept

x86/hvm: unify stdvga mmio intercept with standard mmio intercept

It's clear from the following check in hvmemul_rep_movs:

    if ( sp2mt == p2m_mmio_direct || dp2mt == p2m_mmio_direct ||
         (sp2mt == p2m_mmio_dm && dp2mt == p2m_mmio_dm) )
        return X86EMUL_UNHANDLEABLE;

that mmio <-> mmio copy is not handled. This means the code in the
stdvga mmio intercept that explicitly handles mmio <-> mmio copy when
hvm_copy_to/from_guest_phys() fails is never going to be executed.

This patch therefore adds a check in hvmemul_do_io_addr() to make sure
mmio <-> mmio is disallowed and then registers standard mmio intercept ops
in stdvga_init().

With this patch all mmio and portio handled within Xen now goes through
process_io_intercept().

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>