cmake-native: use internal cmcurl library

This commit is for breaking circular dependency in following condition:
After enabling PACKAGECONFIG nghttp2 for curl, the dependency chain is:
curl-native -> nghttp2-native -> cmake-native -> curl-native.
So change to use internal cmcurl library to fix this. And as using
system curl library before, disable nghttp2 and use system openssl
library for cmcurl.

Signed-off-by: Changqing Li <changqing.li@windriver.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>