x86: Add "make tinyconfig" to configure the tiniest possible kernel

Since commit 5d2acfc7 ("kconfig: make
allnoconfig disable options behind EMBEDDED and EXPERT") in 3.15-rc1,
"make allnoconfig" disables every possible config option.

However, a few configuration options (CC_OPTIMIZE_FOR_SIZE,
OPTIMIZE_INLINING) produce a smaller kernel when turned on, and a few
choices exist (compression, highmem, allocator) for which a non-default
option produces a smaller kernel.

Add a "tinyconfig" option, which starts from allnoconfig and then sets
these options to configure the tiniest possible kernel.  This provides a
better baseline for embedded systems or efforts to reduce kernel size.
Signed-off-by: Josh Triplett <josh@joshtriplett.org>

arch/x86/configs/tiny.config

+CONFIG_NOHIGHMEM=y

kernel/configs/tiny.config

+CONFIG_CC_OPTIMIZE_FOR_SIZE=y
+CONFIG_KERNEL_XZ=y
+CONFIG_OPTIMIZE_INLINING=y
+CONFIG_SLOB=y

scripts/kconfig/Makefile

@@ -117,6 +117,10 @@ PHONY += kvmconfig
 kvmconfig:
 	$(call mergeconfig,kvm_guest)
 
+PHONY += tinyconfig
+tinyconfig: allnoconfig
+	$(call mergeconfig,tiny)
+
 # Help text used by make help
 help:
 	@echo  '  config	  - Update current config utilising a line-oriented program'
@@ -138,6 +142,7 @@ help:
 	@echo  '  listnewconfig   - List new options'
 	@echo  '  olddefconfig	  - Same as silentoldconfig but sets new symbols to their default value'
 	@echo  '  kvmconfig	  - Enable additional options for guest kernel support'
+	@echo  '  tinyconfig	  - Configure the tiniest possible kernel'
 
 # lxdialog stuff
 check-lxdialog  := $(srctree)/$(src)/lxdialog/check-lxdialog.sh