ext4: skip ext4_init_security() and encryption on ea_inodes

Extended attribute inodes are internal to ext4. Adding encryption/security
related attributes on them would mean dealing with nested calls into ea code.
Since they have no direct exposure to user mode, just avoid creating ea
entries for them.

Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>