x86: Drop support for /proc files when !CONFIG_PROC_FS

arch/x86/kernel/cpu/proc.c only exists to support files in /proc; omit that
file when compiling without CONFIG_PROC_FS.

Saves 645 additional bytes on 32-bit x86 when !CONFIG_PROC_FS:

add/remove: 0/5 grow/shrink: 0/0 up/down: 0/-645 (-645)
function                                     old     new   delta
c_stop                                         1       -      -1
c_next                                        11       -     -11
cpuinfo_op                                    16       -     -16
c_start                                       24       -     -24
show_cpuinfo                                 593       -    -593

Signed-off-by: Josh Triplett <josh@joshtriplett.org>

arch/x86/kernel/cpu/Makefile

@@ -13,10 +13,12 @@ nostackp := $(call cc-option, -fno-stack-protector)
 CFLAGS_common.o := $(nostackp)
 
 obj-y := intel_cacheinfo.o scattered.o topology.o
-obj-y += proc.o capflags.o powerflags.o common.o
+obj-y += capflags.o powerflags.o common.o
 obj-y += rdrand.o
 obj-y += match.o
 
+obj-$(CONFIG_PROC_FS) += proc.o
+
 obj-$(CONFIG_X86_32) += bugs.o
 obj-$(CONFIG_X86_64) += bugs_64.o