Default RetroPad mapping for Saturn cores

[ytguwn]

Describe the bug
It seems the defaults have changed and no longer act as documented:

E.g. controller A, B, C buttons are now mapped to RetroPad B, A, R1 buttons (not Y, B, A as in image from docs)

Expected behavior/changes
Update documentation to match the new default configuration

Additional context
Checked with Beetle Saturn and Yabause cores

[ytguwn]

Sega Dreamcast (Flycast) also needs an update

Controller triggers are now mapped to RetroPad L2, R2 triggers not shoulder buttons