imx:mx6sxsabresd support qspi AHB read

Add CONFIG_SYS_FSL_QSPI_AHB in header file to enable AHB in driver.
In order to count the time, add CONFIG_CMD_TIME.

Using AHB read can improve the the read speed about 30%.

AHB read:
=> time sf read 0x8f800000 0 100000
SF: 1048576 bytes @ 0x0 Read: OK
time: 0.174 seconds

=> time sf read 0x8f800000 1000000 100000
SF: 1048576 bytes @ 0x1000000 Read: OK
time: 0.174 seconds

IP read:
=> time sf read 0x8f800000 0 100000
SF: 1048576 bytes @ 0x0 Read: OK
time: 0.227 seconds

=> time sf read 0x8f800000 1000000 100000
SF: 1048576 bytes @ 0x1000000 Read: OK
time: 0.227 seconds

Note:
Quad read is not supported in driver, now. In my side, using AHB and Quad read
can achieve about 16MB/s. Anyway, I have plan to reimplement the driver using
DTB and DM, then make the code cleaner and more feature can be added.
Signed-off-by: NPeng Fan <Peng.Fan@freescale.com>
Reviewed-by: NJagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>

include/configs/mx6sxsabresd.h

@@ -235,6 +235,8 @@
 /* FLASH and environment organization */
 #define CONFIG_SYS_NO_FLASH
 
+#define CONFIG_CMD_TIME
+
 #define CONFIG_FSL_QSPI
 
 #ifdef CONFIG_FSL_QSPI
@@ -244,6 +246,7 @@
 #define CONFIG_SPI_FLASH_SPANSION
 #define CONFIG_SPI_FLASH_STMICRO
 #define CONFIG_SYS_FSL_QSPI_LE
+#define CONFIG_SYS_FSL_QSPI_AHB
 #ifdef CONFIG_MX6SX_SABRESD_REVA
 #define FSL_QSPI_FLASH_SIZE		SZ_16M
 #else