[build] Provide common ARRAY_SIZE() definition

Several files define the ARRAY_SIZE() macro as used in Linux.  Provide
a common definition for this in include/compiler.h.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/compiler.h

@@ -655,6 +655,13 @@ char __debug_disable(OBJECT) = ( DBGLVL_MAX & ~DBGLVL_DFLT );
 #define barrier() __asm__ __volatile__ ( "" : : : "memory" )
 #endif /* ASSEMBLY */
 
+/**
+ * Array size
+ */
+#ifndef ASSEMBLY
+#define ARRAY_SIZE(array) ( sizeof (array) / sizeof ( (array)[0] ) )
+#endif /* ASSEMBLY */
+
 /**
  * @defgroup licences Licence declarations
  *