drm/amd/display: Make init_hw and init_pipes generic for seamless boot

[Why]
For seamless boot the init_hw sequence must be split into
actual hardware vs pipes, in order to defer pipe initialization to set mode
and skip of pipe-destructive sequences

[How]
made dcn10_init_hw and dcn10_init_pipes generic for future dcns to inherit
deleted dcn20 specific versions. This is part 1 of a 2 partimplementation
of seamless boot

Signed-off-by: Martin Leung <martin.leung@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>