staging: xillybus: remove redundant Kconfig dependency

XILLYBUS_PCIE and XILLYBUS_OF are inside 'if XILLYBUS' already, so there is not
need to depend on XILLYBUS.

Cc: Eli Billauer <eli.billauer@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>