EDAC/igen6: fix core dependency

igen6_edac needs mce_register()/unregister() functions,
so it should depend on X86_MCE (or X86_MCE_INTEL).

That change prevents these build errors:

ld: drivers/edac/igen6_edac.o: in function `igen6_remove':
igen6_edac.c:(.text+0x494): undefined reference to `mce_unregister_decode_chain'
ld: drivers/edac/igen6_edac.o: in function `igen6_probe':
igen6_edac.c:(.text+0xf5b): undefined reference to `mce_register_decode_chain'

Fixes: 10590a9d ("EDAC/igen6: Add EDAC driver for Intel client SoCs using IBECC")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/r/20210619160203.2026-1-rdunlap@infradead.org