Improve debug log

Created by: subdiff

Working on gamescope's usage of libliftoff I need to get good debug logs without too much output at once.

For that repetition of unchanging output is minimized and the format of important output is improved.

Example of the output of one call to liftoff_output_apply after this PR has been merged:

Apply on output 0x55c447db2b50.
Layers on CRTC 62:
  Layer 0x55c447db2a40:
    FB_ID = 108
    zpos = 0
    alpha = 65535
    SRC_X = 0
    SRC_Y = 0
    SRC_W = 3840
    SRC_H = 2160
    CRTC_X = 0
    CRTC_Y = 0
    CRTC_W = 3840
    CRTC_H = 2160
Disabling planes: 55 52 49 46 43 40 71 69 67 65 63 61 58
Performing allocation for plane 55 (1/13)
  Layer 0x55c447db2a40 -> plane 55: applying properties...
  Layer 0x55c447db2a40 -> plane 55: incompatible properties
Performing allocation for plane 61 (12/13)
  Layer 0x55c447db2a40 -> plane 61: applying properties...
  Layer 0x55c447db2a40 -> plane 61: incompatible properties
Performing allocation for plane 58 (13/13)
  Layer 0x55c447db2a40 -> plane 58: applying properties...
  Layer 0x55c447db2a40 -> plane 58: success
Found a better allocation with score=1
Found plane allocation for output 0x55c447db2b50 with score=1
Assigning layers to planes:
  Layer 0x55c447db2a40 -> plane 58