configs/qemu_ppc_mac99: needs host-openssl
The kernel configuration used by the qemu_ppc_mac99_defconfig needs
host-openssl, otherwise it fails to build with:
scripts/extract-cert.c:21:25: fatal error: openssl/bio.h: No such file or directory
Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/269139257
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>