asm: start intrinsics examples

Split userland/arch/<arch>/c/ into inline_asm and intrinsics, and move programs
that don't match either up.

userland/arch/x86_64/intrinsics/README.adoc

@@ -0,0 +1 @@
+https://github.com/cirosantilli/linux-kernel-module-cheat#gcc-intrinsics

userland/arch/x86_64/intrinsics/paddq.c

@@ -0,0 +1,18 @@
+/* https://github.com/cirosantilli/linux-kernel-module-cheat#gcc-intrinsics */
+
+#include <assert.h>
+#include <stdio.h>
+
+#include <x86intrin.h>
+
+int main(void) {
+    __m128i input0 = _mm_set_epi32(1, 2, 3, 4);
+    __m128i input1 = _mm_set_epi32(5, 6, 7, 8);
+    __m128i output = _mm_add_epi32(input0, input1);
+    printf("%d\n", (int)output[3]);
+    assert(output[0] == 6);
+    assert(output[1] == 8);
+    assert(output[2] == 10);
+    assert(output[3] == 12);
+    return 0;
+}