kconfig: check for pkg-config on make {menu,n,g,x}config

kconfig: check for pkg-config on make {menu,n,g,x}config

Each of 'make {menu,n,g,x}config' uses (needs) pkg-config to make sure
that other required files are present and to determine build flags
settings, but none of these check that pkg-config itself is present.
Add a check for all 4 of these targets and update
Documentation/process/changes.rst to mention 'pkg-config'.

Fixes kernel bugzilla #77511:
https://bugzilla.kernel.org/show_bug.cgi?id=77511

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Bjørn Forsman <bjorn.forsman@gmail.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>