Release v6.1

See the files INSTALL.md and README.md in the attached archive for info.

Changes from previous release

• Support for newer Raspberry Pi 5 with BCM2712 stepping D0
• Support for I2S sound on Raspberry Pi 5
• Support for PWM sound on Raspberry Pi 5 and Zero (2) (W)
  (requires external circuit on GPIO12/13)
• WM8960 I2S sound driver revised (better audio quality)
• New option backlight= for cmdline.txt for setting the backlight
  level for the Official 7" Raspberry Pi touchscreen (v1)