rtems: Add rtems_interrupt_local_disable|enable()

Add rtems_interrupt_local_disable|enable() as suggested by Pavel Pisa to
emphasize that interrupts are only disabled on the current processor.
Do not define the rtems_interrupt_disable|enable|flash() macros and
functions on SMP configurations since they don't ensure system wide
mutual exclusion.

c/src/lib/libbsp/shared/bootcard.c

@@ -72,7 +72,7 @@ void boot_card(
    *  Make sure interrupts are disabled.
    */
   (void) bsp_isr_level;
-  rtems_interrupt_disable( bsp_isr_level );
+  rtems_interrupt_local_disable( bsp_isr_level );
 
   bsp_boot_cmdline = cmdline;