KVM: MIPS: Add more MMIO load/store instructions emulation

This patch add more MMIO load/store instructions emulation, which can
be observed in QXL and some other device drivers:

1, LWL, LWR, LDW, LDR, SWL, SWR, SDL and SDR for all MIPS;
2, GSLBX, GSLHX, GSLWX, GSLDX, GSSBX, GSSHX, GSSWX and GSSDX for
   Loongson-3.
Reviewed-by: Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>
Signed-off-by: Huacai Chen <chenhc@lemote.com>
Co-developed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Message-Id: <1590220602-3547-14-git-send-email-chenhc@lemote.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>