arm64: timer: Create timer_get_bootus for bootstage support

Implement timer_get_boot_us() based on available functions to support
bootstage command.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/arch/arm/cpu/armv8/generic_timer.c b/arch/arm/cpu/armv8/generic_timer.c
index 303ba3c..bf07a70 100644
--- a/arch/arm/cpu/armv8/generic_timer.c
+++ b/arch/arm/cpu/armv8/generic_timer.c
@@ -61,3 +61,10 @@
 
 	return ticks;
 }
+
+ulong timer_get_boot_us(void)
+{
+	u64 val = get_ticks() * 1000000;
+
+	return val / get_tbclk();
+}