kconfig: prepend CT-NG's version tag to PKGVERSION

"crosstool-NG-${CT_VERSION}" is currently the default for TOOLCHAIN_PKGVERSION,
and this options is passed as is to --with-pkgversion.

This patch prepends "crosstool-NG ${CT_VERSION}" to TOOLCHAIN_PKGVERSION before
passing it to --with-pkgversion.

Signed-off-by: "Benoît THÉBAUDEAU" <benoit.thebaudeau@advansee.com>

 # Compute M68k-specific values

 CT_DoArchTupleValues() {

     :

 }