target/arm: Add missing entries to excnames[] for log strings

Recent changes have added new EXCP_ values to ARM but forgot
to update the excnames[] array which is used to provide
human-readable strings when printing information about the
exception for debug logging. Add the missing entries, and
add a comment to the list of #defines to help avoid the mistake
being repeated in future.

Backports commit 32b81e620ea562d56ab2733421b5da1082b237a2 from qemu

qemu/target/arm/cpu.h

@@ -61,6 +61,8 @@
 #define EXCP_VFIQ           15
 #define EXCP_SEMIHOST       16   /* semihosting call */
 #define EXCP_NOCP           17   /* v7M NOCP UsageFault */
+#define EXCP_INVSTATE       18   /* v7M INVSTATE UsageFault */
+/* NB: new EXCP_ defines should be added to the excnames[] array too */
 
 #define ARMV7M_EXCP_RESET   1
 #define ARMV7M_EXCP_NMI     2

qemu/target/arm/internals.h

@@ -72,6 +72,8 @@ static const char * const excnames[] = {
     "Virtual IRQ",
     "Virtual FIQ",
     "Semihosting call",
+    "v7M NOCP UsageFault",
+    "v7M INVSTATE UsageFault",
 };
 
 /* Scale factor for generic timers, ie number of ns per tick.