microblaze: Decouple exceptions from interrupts

Exception handling should be enabled at all times during execution to
ensure that exceptions are not ignored which would cause further
problems. This separates use of the exception enable bit from use of the
interrupt enable bit in the machine status register so that they can be
manipulated independently.

bsps/microblaze/microblaze_fpga/start/crtinit.S

@@ -81,6 +81,9 @@ _crtinit:
 #ifndef __rtems__
 	brlid	r15, main					   /* Execute the program */
 #else
+	mfs r3, rmsr
+	ori r3, r3, 0x100					   /* Set Exception Enable MSR flag */
+	mts rmsr, r3
 	brlid	r15, boot_card
 #endif /* __rtems__ */
 	addi	r5, r0, 0