add QSPI memory mapped mode support.  tested.  QSPI may enter and exit memory mapped mode; while in effect, other operations (e.g. command, memory) will fail with -EBUSY.

add QSPI memory mapped mode support.  tested.  QSPI may enter and exit memory mapped mode; while in effect, other operations (e.g. command, memory) will fail with -EBUSY.

VNC: Ignore client framebuffer updates if nothing has changed (we can does this because client requests incremental updates

Fixed const warning