drm/i915/gvt: Make correct handling to vreg BXT_PHY_CTL_FAMILY

drm/i915/gvt: Make correct handling to vreg BXT_PHY_CTL_FAMILY

Guest kernel will write to BXT_PHY_CTL_FAMILY to reset DDI PHY
and pull BXT_PHY_CTL to check PHY status. Previous handling will
set/reset BXT_PHY_CTL of all PHYs at same time on receiving vreg
write to some BXT_PHY_CTL_FAMILY. If some BXT_PHY_CTL is already
enabled, following reset to another BXT_PHY_CTL_FAMILY will clear
the enabled BXT_PHY_CTL, which result in guest kernel print:

-----------------------------------
[drm:intel_ddi_get_hw_state [i915]]
*ERROR* Port B enabled but PHY powered down? (PHY_CTL 00000000)
-----------------------------------

The correct handling should operate BXT_PHY_CTL_FAMILY and
BXT_PHY_CTL on the same DDI.

v2: Use correct reg define. The naming looks confusing, however
    current i915_reg.h bind DPIO_PHY0 to _PHY_CTL_FAMILY_DDI and
    bind DPIO_PHY1 to _PHY_CTL_FAMILY_EDP, pairing to
    _BXT_PHY_CTL_DDI_A and _BXT_PHY_CTL_DDI_B respectively.
v3: v2 incorrectly map _PHY_CTL_FAMILY_EDP to _BXT_PHY_CTL_DDI_A.
    BXT_PHY_CTL() looks up DDI using PORTx but not PHYx. Based on
    DPIO_PHY to DDI mapping, make correct vreg handle to BXT_PHY_CTL
    on receiving vreg write to BXT_PHY_CTL_FAMILY. (He, Min)

Current mapping according to bxt_power_wells:
dpio-common-a:
    >>> DPIO_PHY1
    >>> BXT_DPIO_CMN_A_POWER_DOMAINS
    >>> POWER_DOMAIN_PORT_DDI_A_LANES
    >>> PORT_A

dpio-common-bc:
    >>> DPIO_PHY0
    >>> BXT_DPIO_CMN_BC_POWER_DOMAINS
    >>> POWER_DOMAIN_PORT_DDI_B_LANES | POWER_DOMAIN_PORT_DDI_C_LANES
    >>> PORT_B or PORT_C

Signed-off-by: Colin Xu <colin.xu@intel.com>
Reviewed-by: He, Min <min.he@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>