drm/amd/display: convert link.h functions to function pointer style

[Why & How]
All dc subcomponents should call another dc component via function pointers
stored in a component structure. This is part of dc coding convention since
the beginning. The reason behind this is to improve encapsulation and
polymorphism. The function contract is extracted into a single link service
structure defined in link.h header file and implemented only in link_factory.c instead
of spreading across multiple files in link component file structure.

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drm/amd/display: move dc_link functions in protocols folder to dc_link_exports

[why]
link component should only have one interface serving dc.

[how]
We are moving dc_link functions exposed to DM to dc_link_exports
and unify link component interface in link.h with function pointer
to match the style of other dc component. This is the third step to move
dc_link functions under protocols folder to dc_link_exports.

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drm/amd/display: create accessories, hwss and protocols sub folders in link

[why]
link component contains three sub folders:

accessories - utilities for improving testability, logging or tracing, doesn't impact
end user use cases.

protocols - specs defined protocols used in end user use cases

hwss - hwss owned link_hwss object, served as an abstraction layer in hwss to
access various types of encoder/phy/dpia endpoints in a unified interface.

sooner we will have files directly under link folder one for the implementation of
each major link behavior such as link_create, link_detect, link_validate
and link_set_dpms.

Reviewed-by: George Shen <George.Shen@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>