kern: switch memset to optimized impl

libraries/libmesosphere/source/libc/arch/arm64/memset.arch.arm64.s

@@ -76,11 +76,13 @@ L(set96):
 	.p2align 4
 L(set_long):
 	stp	    val, val, [dstin]
-	bic	    dst, dstin, 15
 #if DC_ZVA_THRESHOLD
 	cmp	    count, DC_ZVA_THRESHOLD
 	ccmp	val, 0, 0, cs
+	bic	    dst, dstin, 15
 	b.eq	L(zva_64)
+#else
+	bic	    dst, dstin, 15
 #endif
 	/* Small-size or non-zero memset does not use DC ZVA. */
 	sub	    count, dstend, dst

libraries/libmesosphere/source/libc/kern_libc_config.arch.arm64.h

@@ -19,6 +19,6 @@
 #define MESOSPHERE_LIBC_MEMCPY_GENERIC  0
 #define MESOSPHERE_LIBC_MEMCMP_GENERIC  0
 #define MESOSPHERE_LIBC_MEMMOVE_GENERIC 0
-#define MESOSPHERE_LIBC_MEMSET_GENERIC  1
+#define MESOSPHERE_LIBC_MEMSET_GENERIC  0
 #define MESOSPHERE_LIBC_STRNCPY_GENERIC 1
-#define MESOSPHERE_LIBC_STRNCMP_GENERIC 1
+#define MESOSPHERE_LIBC_STRNCMP_GENERIC 1

libraries/libmesosphere/source/libc/kern_libc_config.h

@@ -23,4 +23,4 @@
 
     #error "Unknown architecture for libc"
 
-#endif
+#endif