libcflat: add SZ_1M and SZ_2G

Add SZ_1M and SZ_2G to libcflat.h

s390x needs those for large/huge pages

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20210611140705.553307-3-imbrenda@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>