Adding ability for hal keymaster to read vendor SPL

Keymaster hal needs to be able to read the vendor SPL for purposes of
rollback protection.

Test: Keymaster can access the hal_keymaster_default property
Change-Id: Ifa53adb23f6ab79346e9dd9616b34d8b24395a0a

vendor/hal_keymaster_default.te

@@ -3,3 +3,5 @@ hal_server_domain(hal_keymaster_default, hal_keymaster)
 
 type hal_keymaster_default_exec, exec_type, vendor_file_type, file_type;
 init_daemon_domain(hal_keymaster_default)
+
+get_prop(hal_keymaster_default, vendor_security_patch_level_prop);