staging: fbtft: Make framebuffer registration message debug-only

The framebuffer registration message is informational only and not
useful during normal operation. Convert it to debug-level logging to
keep the driver quiet when working correctly.

Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Chintan Patel <chintanlike@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>