agx: Add AGX_MESA_DEBUG=nopreamble option

Useful both for ruling out issues with shader preambles as well as (in some
cases) making for a nicer reading experience of the compiled assembly.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21430>

src/asahi/compiler/agx_compiler.h

@@ -48,6 +48,7 @@ enum agx_dbg {
    AGX_DBG_NOVALIDATE  = BITFIELD_BIT(5),
    AGX_DBG_NOOPT       = BITFIELD_BIT(6),
    AGX_DBG_WAIT        = BITFIELD_BIT(7),
+   AGX_DBG_NOPREAMBLE  = BITFIELD_BIT(8),
 };
 /* clang-format on */