arm: imx-common: introduce back usec2ticks

This commit "2bb01482"
do some clean up to use the code in lib/time.c.
But usec2ticks is still being used by security related job ring code.
Bring back the function to avoid build break when CONFIG_FSL_CAAM
is defined.
The computation logic has been changed, using 64-bit variable
to ease the process, making it work on older (MX5) platforms.

Signed-off-by: Peng Fan <van.freenix@gmail.com>
Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
Signed-off-by: Gary Bisson <gary.bisson@boundarydevices.com>

arch/arm/imx-common/timer.c

@@ -120,3 +120,19 @@ ulong get_tbclk(void)
 {
 	return gpt_get_clk();
 }
+
+/*
+ * This function is intended for SHORT delays only.
+ * It will overflow at around 10 seconds @ 400MHz,
+ * or 20 seconds @ 200MHz.
+ */
+unsigned long usec2ticks(unsigned long _usec)
+{
+	unsigned long long usec = _usec;
+
+	usec *= get_tbclk();
+	usec += 999999;
+	do_div(usec, 1000000);
+
+	return usec;
+}