intel: Add function to check fpga readiness

Create a function to check for fpga readiness, and move the checking out
of bridge enable function.

Signed-off-by: Hadi Asyrafi <muhammad.hadi.asyrafi.abdul.halim@intel.com>
Change-Id: I3f473ffeffa9ce181a48977560c8bda19c6123c0
diff --git a/plat/intel/soc/common/include/socfpga_mailbox.h b/plat/intel/soc/common/include/socfpga_mailbox.h
index c5f2fbe..c4b9e59 100644
--- a/plat/intel/soc/common/include/socfpga_mailbox.h
+++ b/plat/intel/soc/common/include/socfpga_mailbox.h
@@ -120,5 +120,6 @@
 void mailbox_clear_response(void);
 
 uint32_t intel_mailbox_get_config_status(uint32_t cmd);
+int intel_mailbox_is_fpga_not_ready(void);
 
 #endif /* SOCFPGA_MBOX_H */