timer: stm32: migrate trace to log macro

Define LOG_CATEGORY to allow filtering with log command.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>

drivers/timer/stm32_timer.c

@@ -4,6 +4,8 @@
  * Author(s): Patrice Chotard, <patrice.chotard@foss.st.com> for STMicroelectronics.
  */
 
+#define LOG_CATEGORY UCLASS_TIMER
+
 #include <common.h>
 #include <clk.h>
 #include <dm.h>