[kernel][dev][interrupt] C -> CPP conversion

Minimal modifications.

Change-Id: Ia2ec00fcc134af34afcf21423eb209ebc8baf735
Tested: make sure still builds on ARM.
diff --git a/kernel/dev/interrupt/msi.c b/kernel/dev/interrupt/msi.cpp
similarity index 93%
rename from kernel/dev/interrupt/msi.c
rename to kernel/dev/interrupt/msi.cpp
index 03ba712..8d3b99d 100644
--- a/kernel/dev/interrupt/msi.c
+++ b/kernel/dev/interrupt/msi.cpp
@@ -8,16 +8,17 @@
 // support so that individual platforms do not need to provide
 // them if they only partially support MSI.
 
+#include <dev/interrupt.h>
+
 #include <stdbool.h>
 #include <zircon/compiler.h>
 #include <zircon/types.h>
-#include <dev/interrupt.h>
 
-__WEAK bool msi_is_supported(void) {
+__WEAK bool msi_is_supported() {
     return false;
 }
 
-__WEAK bool msi_supports_masking(void) {
+__WEAK bool msi_supports_masking() {
     return false;
 }
 
diff --git a/kernel/dev/interrupt/rules.mk b/kernel/dev/interrupt/rules.mk
index dc2ff4c..42d7b00 100644
--- a/kernel/dev/interrupt/rules.mk
+++ b/kernel/dev/interrupt/rules.mk
@@ -9,6 +9,6 @@
 MODULE := $(LOCAL_DIR)
 
 MODULE_SRCS := \
-    $(LOCAL_DIR)/msi.c
+    $(LOCAL_DIR)/msi.cpp
 
 include make/module.mk