libpayload: Catch exceptions and print out an error message.

Give some indication what happened instead of just crashing.
As part of setup, cause an exception and make sure that we get
the right one, and that we recover correctly. Hence we have
some assurance that if they really happen we can handle them.

Built and booted into test payload on Snow. Saw the built in test function
worked correctly. Artificially added code which got an exception and saw that
the error information prints correctly.

Change-Id: I2e0d022f090ee422fb988074fbb197afa2485caa
Signed-off-by: Gabe Black <gabeblack@google.com>
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: http://review.coreboot.org/2569
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins)

payloads/libpayload/arch/armv7/main.c

@@ -27,6 +27,7 @@
  * SUCH DAMAGE.
  */
 
+#include <arch/exception.h>
 #include <libpayload.h>
 
 unsigned int main_argc;    /**< The argc value to pass to main() */
@@ -51,6 +52,8 @@ void start_main(void)
 	console_init();
 #endif
 
+	exception_init();
+
 	/*
 	 * Any other system init that has to happen before the
 	 * user gets control goes here.