drm/amd/display: Fix reg timeout in enc314_enable_fifo

[Why]
The link enablement sequence can end up resetting the encoder while
the PHY symclk isn't yet on.

This means that waiting for symclk on will timeout, along with the reset
bit never asserting high.

This causes unnecessary delay when enabling the link and produces a
warning affecting multiple IGT tests.

[How]
Don't wait for the symclk to be on here because firmware already does.

Don't wait for reset if we know the symclk isn't on.

Split the reset into a helper function that checks the bit and decides
whether or not a delay is sufficient.

Reviewed-by: Roman Li <Roman.Li@amd.com>
Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org # 6.0.x