Bug fix to UFS/FFS superblock integrity checks when reading a superblock.

The tests for number of cylinder groups (fs_ncg), inodes per cylinder
group (fs_ipg), and the size and layout of the cylinder group summary
information (fs_csaddr and fs_cssize) were overly restrictive and
would exclude some valid filesystems. These updates avoid precluding
valid fiesystems while still detecting rogue values that can crash or
hang the kernel.

Reported by: Chuck Silvers
Tested by: Peter Holm
MFC after: 1 month (with 076002f24d35)
Differential Revision: https://reviews.freebsd.org/D35219