kbuild: Additional config targets for testing

kbuild: Additional config targets for testing

This patch adds the following targets, which generate some configs
useful for testing - which kind should be clear from the names:

o allyesconfig
o allmodconfig
o allnoconfig
o randconfig

It also adds

o defconfig

which does the same as make oldconfig but uses the defaults for all
new options without asking.

The actual patch was done by Ghozlane Toumi, maintained in kbuild-2.5
by Keith Owens, and extracted by Sam Ravnborg and patch@luckynet.dynu.com.