drm/i915/display/tgl+: Set default values for all registers in PIPE_MBUS_DBOX_CTL

MBUS_DBOX_B2B_TRANSACTIONS_MAX, MBUS_DBOX_B2B_TRANSACTIONS_DELAY and
MBUS_DBOX_REGULATE_B2B_TRANSACTIONS_EN were being programmed with
zeros while specification has different default values for this
registers in display 12 and newer.

While at it also converting all MBUS_DBOX macros to use REG_* macros.

BSpec: 50343
BSpec: 20231
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220330155724.255226-1-jose.souza@intel.com