Add gettime command

Gettime returns the current timer value.  If CONFIG_SYS_HZ is defined
then the timer value is also converted to seconds.

Tegra20 (SeaBoard) # gettime
Timer val: 7754
Seconds : 7
Remainder : 754
sys_hz = 1000

There has been some discussion about whether this is useful enough to
be included in U-Boot. The following boards do not have CONFIG_SYS_HZ
defined:

M52277EVB
M52277EVB_stmicro
M53017EVB
M54418TWR
M54418TWR_nand_mii
M54418TWR_nand_rmii
M54418TWR_nand_rmii_lowfreq
M54418TWR_serial_mii
M54418TWR_serial_rmii

Signed-off-by: Anton Staaf <robotboy@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/README b/README
index 5a86ae9..d1c60de 100644
--- a/README
+++ b/README
@@ -824,6 +824,7 @@
 		CONFIG_CMD_FDOS		* Dos diskette Support
 		CONFIG_CMD_FLASH	  flinfo, erase, protect
 		CONFIG_CMD_FPGA		  FPGA device initialization support
+		CONFIG_CMD_GETTIME	* Get time since boot
 		CONFIG_CMD_GO		* the 'go' command (exec code)
 		CONFIG_CMD_GREPENV	* search environment
 		CONFIG_CMD_HWFLOW	* RTS/CTS hw flow control