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

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 <[email protected]>
Signed-off-by: Huacai Chen <[email protected]>
Co-developed-by: Jiaxun Yang <[email protected]>
Message-Id: <1590220602[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>