drm/xe: Define xe_reg_is_valid

Add a function to check if struct xe_reg has valid address.

v2:
 - Rebase.
 - Make xe_reg_is_valid as inline function instead of a macro. (Badal).
 - Update commit msg.

Signed-off-by: Karthik Poosa <karthik.poosa@intel.com>
Suggested-by: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Badal Nilawar <badal.nilawar@intel.com>
Reviewed-by: Badal Nilawar <badal.nilawar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240405130127.1392426-2-karthik.poosa@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>

drivers/gpu/drm/xe/regs/xe_reg_defs.h

@@ -131,4 +131,9 @@ struct xe_reg_mcr {
 				 .__reg = XE_REG_INITIALIZER(r_,  ##__VA_ARGS__, .mcr = 1)	\
 				 })
 
+static inline bool xe_reg_is_valid(struct xe_reg r)
+{
+	return r.addr;
+}
+
 #endif