drm/amd/display: Flatten unnecessary i2c functions

drm/amd/display: Flatten unnecessary i2c functions

[Why]
The dce_i2c_hw code contained four funtcions that were only
called in one place and did not have a clearly delineated
purpose.

[How]
Inline these functions, keeping the same functionality.

This is not a functional change.

The functions disable_i2c_hw_engine and release_engine_dce_hw were
pulled into their respective callers.

The most interesting part of this change is the acquire functions.
dce_i2c_hw_engine_acquire_engine was pulled into
dce_i2c_engine_acquire_hw, and dce_i2c_engine_acquire_hw was pulled
into acquire_i2c_hw_engine.

Some notes to show that this change is not functional:
-Failure conditions in any function resulted in a cascade of calls that
ended in a 'return NULL'.
Those are replaced with a direct 'return NULL'.

-The variable result is the one from dce_i2c_hw_engine_acquire_engine.
The boolean result used as part of return logic was removed.

-As the second half of dce_i2c_hw_engine_acquire_engine is only executed
if that function is returning true and therefore exiting the do-while
loop in dce_i2c_engine_acquire_hw, those lines were moved outside
of the loop.

Signed-off-by: David Francis <David.Francis@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>