s390/bpf: add dependency to z196 features

The new ebpf code uses e.g. the laal instruction which is part of the
interlocked-access facility 1 which again was introduced with z196.

So we must make sure the ebpf code generator depends on MARCH_Z196_FEATURES.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>