Raw images contain supplementary information like synchronization fields,
correction codes etc. that needs to be ignored/discarded when
reading/writing user data.
This commit establish a basic architecture for exchanging user data
between a virtual device and a raw image.
The RR0_RX_CHARACTER_AVAILABLE bit is cleared after the character is read in receive_byte, but clear it anyway in read_reg when there's no character available just in case a character that was available somehow becomes unavailable.
Normally, the Port_B_Data or Port_A_Data address is used to directly access RR8 or WR8, but setting the register pointer in Port_B_Cmd or Port_A_Cmd to RR8/WR8 is another option.
Update write_regs[WR8] and read_regs[RR8] for possible debugging purposes.
Update write_regs[WR9] even though most or all of the bits are in master_int_cntrl.
Fix hardware reset for WR9. It's supposed to leave WR9_NO_VECTOR | WR9_VECTOR_INCLUDES_STATUS unchanged.
Fix channel reset for WR9. It's supposed to clear WR9_INTERRUPT_MASKING_WITHOUT_INTACK.
Add absolute coordinates for tablets. Absolute coordinates is relative to window so it can't work for multiple displays? Doesn't work for single display without mouse driver modification.
Add arbitrary number of buttons. Previously, only one mouse button was supported.
Add arbitrary number of bits. Previously, only 7 bits per axis was supported which is good enough for relative movement but not absolute movement.
Allow the dbdma program to initiate reading/writing by adding in and out callbacks.
Support the DBDMA flush command by adding a flush callback. If the transfer completes, then clear the flush flag, otherwise leave it unchanged.
Clear the flush flag after it is copied to the xferStatus of the DBDMA command.
