Add pkg-config to required deps for autogen

Otherwise I get the following error:

```
configure.ac:692: warning: macro 'AM_PATH_LIBGCRYPT' not found in library
configure.ac:43: error: possibly undefined macro: AC_DEFINE
      If this token and others are legitimate, please use m4_pattern_allow.
      See the Autoconf documentation.
configure.ac:48: error: possibly undefined macro: AC_MSG_ERROR
configure.ac:278: error: *** pkg.m4 missing, please install pkg-config
configure.ac:407: error: *** pkg.m4 missing, please install pkg-config
configure.ac:692: error: possibly undefined macro: AM_PATH_LIBGCRYPT
configure.ac:1261: error: *** pkg.m4 missing, please install pkg-config
autoreconf: /usr/bin/autoconf failed with exit status: 1
```