linuxkpi: Add spin_trylock_irqsave() macro

This is needed by the drm-kmod 5.6 update.

Reviewed by:		hselasky
MFC after:		3 days
Differential Revision:	https://reviews.freebsd.org/D30706

sys/compat/linuxkpi/common/include/linux/spinlock.h

@@ -104,6 +104,11 @@ typedef struct {
 #define	spin_trylock_irq(_l)			\
 	spin_trylock(_l)
 
+#define	spin_trylock_irqsave(_l, flags) ({	\
+	(flags) = 0;				\
+	spin_trylock(_l);			\
+})
+
 #define	spin_lock_nested(_l, _n) do {		\
 	if (SPIN_SKIP())			\
 		break;				\