drm/i915/gvt: Remove reduntant printing of untracked mmio

Reduntant message prints when:
  - linux guest creating.
  - dma-buf win10 guest boot.
  - xonotic stress testing in linux guest.

Add below registers to default MMIO handler:
    0xd00, RPM_CONFIG0
    0xd40, RC6_LOCATION
    0x65010, HSW_AUD_MISC_CTRL
    0x6671c,
    0x700a0, CUR_FBC_CTL
    0x7239c,

v2:
  - Should init i915_reg_t using uint32_t instead of _MMIO macro.
    (compiling errors)
  - Use defined offset in i915_reg.h
    (zhenyu)

Signed-off-by: Colin Xu <colin.xu@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>