drm: implement syncobj and fence for VIRGL/VirtIO driver

Extract protocol-agnostic FenceTimeline from Intel to shared
src/drivers/fence.rs — atomic-based fence tracking suitable
for Intel, VIRGL, and AMD drivers.

Extract protocol-agnostic SyncobjManager from Intel to shared
src/drivers/syncobj.rs — syncobj create/destroy/signal/reset/
wait/query and sync_file fd export/import.

Wire both into VirtioDriver:
- Add FenceTimeline + SyncobjManager fields
- Implement all 5 GpuDriver syncobj trait methods
  (create, destroy, wait, export_fd, import_fd)
- Track fence seqnos in virgl_submit_3d (allocate
  before submit, signal after completion)

Intel fence.rs and syncobj.rs converted to thin re-export
modules pointing at shared sources — no behavioral change
for Intel driver.

This gives Mesa VIRGL userspace the standard DRM syncobj
API for GPU/compositor synchronization.

recipes/tools/file/source/magic/Magdir/bytecode

@@ -0,0 +1,41 @@
+
+#------------------------------------------------------------
+# $File: bytecode,v 1.5 2023/02/20 16:25:05 christos Exp $
+# magic for various bytecodes
+
+# From: Mikhail Gusarov <dottedmag@dottedmag.net>
+# NekoVM (https://nekovm.org/) bytecode
+0	string		NEKO	NekoVM bytecode
+>4	lelong		x	(%d global symbols,
+>8	lelong		x	%d global fields,
+>12	lelong		x	%d bytecode ops)
+!:mime	application/x-nekovm-bytecode
+
+# https://www.iana.org/assignments/media-types/application/vnd.resilient.logic
+# From: Benedikt Muessig <benedikt@resilient-group.de>
+0	belong		0x07524c4d	Resilient Logic bytecode
+!:mime	application/vnd.resilient.logic
+>4	byte/16		x	\b, version %d
+>4	byte&0x0f	x	\b.%d
+
+# Guile file magic from <dalepsmith@gmail.com>
+# https://www.gnu.org/s/guile/
+# https://git.savannah.gnu.org/gitweb/?p=guile.git;f=libguile/_scm.h;hb=HEAD#l250
+
+0	string	GOOF----	Guile Object
+>8	string	LE		\b, little endian
+>8	string	BE		\b, big endian
+>11	string	4		\b, 32bit
+>11	string	8		\b, 64bit
+>13	regex	.\\..		\b, bytecode v%s
+
+# Racket file magic
+# From: Haelwenn (lanodan) Monnier <contact+libmagic@hacktivis.me>
+# https://racket-lang.org/
+# https://github.com/racket/racket/blob/master/racket/src/expander/compile/write-linklet.rkt
+0	string	#~
+>&0	pstring	x
+>>&0	pstring	racket
+>>>0	string	#~	Racket bytecode
+>>>>&0	pstring	x       (version %s)
+