asahi: Add nomsaa debug flag

This forces off MSAA, which together with smalltile mode helps test more
combinations.

Signed-off-by: Asahi Lina <lina@asahilina.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24258>

src/asahi/lib/agx_device.h

@@ -28,6 +28,7 @@ enum agx_dbg {
    AGX_DBG_NOWC = BITFIELD_BIT(12),
    AGX_DBG_SYNCTVB = BITFIELD_BIT(13),
    AGX_DBG_SMALLTILE = BITFIELD_BIT(14),
+   AGX_DBG_NOMSAA = BITFIELD_BIT(15),
 };
 
 /* Dummy partial declarations, pending real UAPI */

src/gallium/drivers/asahi/agx_pipe.c

@@ -66,6 +66,7 @@ static const struct debug_named_value agx_debug_options[] = {
    {"nowc",      AGX_DBG_NOWC,     "Disable write-combining"},
    {"synctvb",   AGX_DBG_SYNCTVB,  "Synchronous TVB growth"},
    {"smalltile", AGX_DBG_SMALLTILE,"Force 16x16 tiles"},
+   {"nomsaa",    AGX_DBG_NOMSAA,   "Force disable MSAA"},
    DEBUG_NAMED_VALUE_END
 };
 /* clang-format on */
@@ -1884,6 +1885,9 @@ agx_is_format_supported(struct pipe_screen *pscreen, enum pipe_format format,
    if (sample_count > 1 && sample_count != 4 && sample_count != 2)
       return false;
 
+   if (sample_count > 1 && agx_device(pscreen)->debug & AGX_DBG_NOMSAA)
+      return false;
+
    if (MAX2(sample_count, 1) != MAX2(storage_sample_count, 1))
       return false;