package/uclibc: defconfig: enable sha-256/512 password auth support

package/uclibc: defconfig: enable sha-256/512 password auth support

As recently reported on the mailing list:
http://lists.busybox.net/pipermail/buildroot/2016-February/154130.html

Our configuration options to use sha-256 / sha-512 password encoding do not
work very well with uClibc-ng as our defconfig doesn't enable support for
these encodings, breaking E.G. password login with dropbear.

Notice that it doesn't break login with the busybox login applet, as we
currently force the use of the internal busybox password handling routines
when sha-256/512 encoding is used. This workaround can afaik now be removed.

To fix this, enable support for these password encodings in our defconfig.
Do it unconditionally and not based on BR2_TARGET_GENERIC_PASSWD_* so it
also works when a Buildroot toolchain is reused as an external toolchain and
as the support code is quite small (~8KB):

-rwxr-xr-x 1 peko peko 13360 Mar  7 22:56 output/target/lib/libcrypt-1.0.12.so
-rwxr-xr-x 1 peko peko 21552 Mar  7 23:47 output-sha/target/lib/libcrypt-1.0.12.so

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Acked-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>