drm/amd/display: Fix out-of-bound accesses

[WHAT & HOW]
hpo_stream_to_link_encoder_mapping has size MAX_HPO_DP2_ENCODERS(=4),
but location can have size up to 6. As a result, it is necessary to
check location against MAX_HPO_DP2_ENCODERS.

Similiarly, disp_cfg_stream_location can be used as an array index which
should be 0..5, so the ASSERT's conditions should be less without equal.

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3904


Reviewed-by: Austin Zheng <Austin.Zheng@amd.com>
Reviewed-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>