drm/amd/display: Move power control from link encoder to hwsequencer

A recent commit moved the backlight control code along with the register
defines, but did not move the power control code. This along with
remnant fields in the dce110_link_enc_registers struct made it so that
the code still compiled, but any attempts to access the
LVTMA_PWRSEQ_STATE register led to reading from an address of 0. This
patch corrects that.

Also, rename blacklight_control to edp_backlight_control (Typo fix).

Signed-off-by: Andrew Jiang <Andrew.Jiang@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>