Unify our assembler macros.

Our <machine/asm.h> files were modified from upstream, to the extent
that no architecture was actually using the upstream ENTRY or END macros,
assuming that architecture even had such a macro upstream. This patch moves
everyone to the same macros, with just a few tweaks remaining in the
<machine/asm.h> files, which no one should now use directly.

I've removed most of the unused cruft from the <machine/asm.h> files, though
there's still rather a lot in the mips/mips64 ones.

Bug: 12229603
Change-Id: I2fff287dc571ac1087abe9070362fb9420d85d6d
diff --git a/libc/arch-arm/bionic/_setjmp.S b/libc/arch-arm/bionic/_setjmp.S
index 239947e..64a0a31 100644
--- a/libc/arch-arm/bionic/_setjmp.S
+++ b/libc/arch-arm/bionic/_setjmp.S
@@ -34,7 +34,7 @@
  * SUCH DAMAGE.
  */
 
-#include <machine/asm.h>
+#include <private/bionic_asm.h>
 #include <machine/setjmp.h>
 #include <machine/cpu-features.h>