usb: sisusb_con, cleanup configs

There are two macros defined:
1) ifdef CONFIG_COMPAT => define SISUSB_NEW_CONFIG_COMPAT
2) ifdef CONFIG_USB_SISUSBVGA_CON => define INCL_SISUSB_CON

Remove the latter and make use only of the former. This removes one
layer of obfuscation.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>