staging: unisys: Fix broken build when ARCH=um

When building with ARCH=um you get the following error:

arch/x86/include/asm/cpufeature.h:252:42: error: 'REQUIRED_MASK0'
	undeclared

The Unisys drivers should not be compiled for UML, so this patch addresses
that by adding a dependency to kconfig for !UML.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Tested-by: Ken Cox <jkc@redhat.com>
Signed-off-by: Ken Cox <jkc@redhat.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>