python/python3: add virtual/crypt to DEPENDS

python/python3: add virtual/crypt to DEPENDS

Since  `6146b8c glibc: Disable crypt support in glibc' in oe-core,
python2/3 could not find symbol crypt which caused import crypt failed.
[snip]
>>> import crypt
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python3.5/crypt.py", line 3, in <module>
    import _crypt
ImportError: /usr/lib64/python3.5/lib-dynload/_crypt.cpython-35m-x86_64-linux-gnu.so: undefined symbol: crypt
[snip]

Add virtual/crypt to DEPENDS, and python's build system (setup.py)
will search libcrypt.so in recipe-sysroot and add `-lcrypt' if it
exists.

(From OE-Core rev: d2a929d932900f753af1a06a8cb98d953369e3b4)

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>