package/ecryptfs-utils: add host-pkgconf dependency

Add host-pkgconf dependency to fix the following build failure (e.g. with
BR2_PER_PACKAGE_DIRECTORIES):

configure: error: OpenSSL not found

As a side-effect, NSS_{CFLAGS,LIBS} can be dropped

Fixes:
 - http://autobuild.buildroot.org/results/ea16957e8f048b713f5d2713aa5f0c157b62f574



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>