cml1.bbclass: Handle ncurses-native being available via pkg-config

The linux kernel will by default use pkg-config to get ncurses(w) paths,
falling back to absolute path checks otherwise. If the build host does
not have ncurses installed this will fail as pkg-config will not search
the native sysroot for ncurses.

To more all kernel/kconfig sources, inject the equivalent native
pkg-config variables similar to what is done by the pkg-config-native
script. This only affects the menuconfig python task itself and the
oe_terminal call inside it.

Signed-off-by: Nathan Rossi <nathan@nathanrossi.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>