mfd: cs5535: Don't build on UML

The cs5535-mfd driver uses CPU-specific data that is not available
for ARCH=um builds, so don't allow it to be built for UML.

Prevents these build errors:

In file included from ../arch/x86/include/asm/olpc.h:7,
                 from ../drivers/mfd/cs5535-mfd.c:17:
../arch/x86/include/asm/geode.h: In function ‘is_geode_gx’:
../arch/x86/include/asm/geode.h:16:31: error: ‘struct cpuinfo_um’ has no member named ‘x86_vendor’
   16 |         return ((boot_cpu_data.x86_vendor == X86_VENDOR_NSC) &&
../arch/x86/include/asm/geode.h:16:46: error: ‘X86_VENDOR_NSC’ undeclared (first use in this function); did you mean ‘X86_VENDOR_ANY’?
   16 |         return ((boot_cpu_data.x86_vendor == X86_VENDOR_NSC) &&
../arch/x86/include/asm/geode.h:17:31: error: ‘struct cpuinfo_um’ has no member named ‘x86’
   17 |                 (boot_cpu_data.x86 == 5) &&
../arch/x86/include/asm/geode.h:18:31: error: ‘struct cpuinfo_um’ has no member named ‘x86_model’
   18 |                 (boot_cpu_data.x86_model == 5));
../arch/x86/include/asm/geode.h: In function ‘is_geode_lx’:
../arch/x86/include/asm/geode.h:23:31: error: ‘struct cpuinfo_um’ has no member named ‘x86_vendor’
   23 |         return ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) &&
../arch/x86/include/asm/geode.h:23:46: error: ‘X86_VENDOR_AMD’ undeclared (first use in this function); did you mean ‘X86_VENDOR_ANY’?
   23 |         return ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) &&
../arch/x86/include/asm/geode.h:24:31: error: ‘struct cpuinfo_um’ has no member named ‘x86’
   24 |                 (boot_cpu_data.x86 == 5) &&
../arch/x86/include/asm/geode.h:25:31: error: ‘struct cpuinfo_um’ has no member named ‘x86_model’
   25 |                 (boot_cpu_data.x86_model == 10));

Fixes: 68f5d3f3 ("um: add PCI over virtio emulation driver")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20221201012541.11809-1-rdunlap@infradead.org