polarssl: add dependency openssl

polarssl compiles with openssl to build unit test cases. If openssl
doesn't exist, native libssl.so will be used. Then causes error:

| .../bitbake_build/tmp/sysroots/x86_64-linux/usr/lib/libssl.so: error adding symbols: File in wrong format

Add dependency openssl for polarssl to fix it.

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Mark Hatle <mark.hatle@windriver.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>