arch: add some defines for generic timer registers

Those defines are used in STM32MP1 clock driver.
It is better to put them altogether with already defined registers.

Change-Id: I6f8ad8c2477b947af6f76283a4ef5c40212d0027
Signed-off-by: Yann Gautier <yann.gautier@st.com>
diff --git a/include/arch/aarch64/arch.h b/include/arch/aarch64/arch.h
index d23d89e..502b868 100644
--- a/include/arch/aarch64/arch.h
+++ b/include/arch/aarch64/arch.h
@@ -99,6 +99,7 @@
  * Generic timer memory mapped registers & offsets
  ******************************************************************************/
 #define CNTCR_OFF			U(0x000)
+#define CNTCV_OFF			U(0x008)
 #define CNTFID_OFF			U(0x020)
 
 #define CNTCR_EN			(U(1) << 0)