openrisc: Set CONFIG_MULTI_IRQ_HANDLER

arm has an optional MULTI_IRQ_HANDLER, which openrisc copied but didn't
make optional.  The multi irq handler infrastructure has been copied to
generic code selectable with a new config symbol. That symbol can be
selected by randconfig builds and can cause build breakage.

Introduce CONFIG_MULTI_IRQ_HANDLER as an intermediate step which prevents
the core config symbol from being selected. The openrisc local config
symbol will be removed once openrisc gets converted to the generic code.
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Link: https://lkml.kernel.org/r/20180404043130.31277-3-palmer@sifive.com

arch/openrisc/Kconfig

@@ -27,6 +27,7 @@ config OPENRISC
 	select GENERIC_STRNLEN_USER
 	select GENERIC_SMP_IDLE_THREAD
 	select MODULES_USE_ELF_RELA
+	select MULTI_IRQ_HANDLER
 	select HAVE_DEBUG_STACKOVERFLOW
 	select OR1K_PIC
 	select CPU_NO_EFFICIENT_FFS if !OPENRISC_HAVE_INST_FF1
@@ -68,6 +69,9 @@ config STACKTRACE_SUPPORT
 config LOCKDEP_SUPPORT
 	def_bool  y
 
+config MULTI_IRQ_HANDLER
+	def_bool y
+
 source "init/Kconfig"
 
 source "kernel/Kconfig.freezer"