[Why]
irq service requires changes for DCE6 support

[How]
(v1) DCE6 targets are added replicating existing DCE8 implementation.
     due to missing CRTC_VERTICAL_INTERRUPT0_CONTROL registers/masks,
     dce/dce_8_0_{d,sh_mask}.h used instead of dce/dce_6_0_{d,sh_mask}.h

(v2) DCE6 headers used adding the necessary vblank irq registers
     (INT_MASK and VBLANK_STATUS) and vblank irq masks as implemented
     in amdgpu driver.
     Add vblank_irq_info_funcs_dce60 with .set and .ack as per commit
     b10d51f8 ("drm/amd/display: Add interrupt entries for VBLANK isr.")
     and use it in vblank_int_entry(reg_num) macro definition

(v3) updated due to following kernel 5.3 commit:
     4fc4dca8 ("drm/amd: drop use of drmp.h in os_types.h")

(v4) updated due to following kernel 5.6 commit:
     d9e32672 ("drm/amd/display: cleanup of construct and destruct funcs")
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Mauro Rossi <issor.oruam@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>