Teletext fixes
Jeffrey Lee authored
Detail:
  s/vdu/vdudriver, s/vdu/vdumodes - Re-introduce TTX256 so that 8bpp teletext will be used if no MDF is loaded
  s/vdu/vdudriver - If the video driver didn't support the native mode 7 colour depth, ModePromoTable was swapping it for another mode number, preventing the AltTTX code in FindOKMode from operating. So, skip the ModePromoTable check for mode 7.
  s/vdu/vduswis - Minor correction to alternate teletext mode search; 1<<5 = 32bpp, so stop search at log2bpp of 6
Admin:
  Tested on Raspberry Pi


Version 5.74. Retagged as 'Kernel-5_74'
89fa2c01