bsp/imx: Add an extra ecspi clock.

Some imx chips or boards don't use the same frequency for ECSPI and IPG.

Update #3869

bsps/arm/imx/include/arm/freescale/imx/imx_ccmvar.h

@@ -48,6 +48,9 @@ uint32_t imx_ccm_perclk_hz(void);
 uint32_t imx_ccm_sdhci_hz(void);
 uint32_t imx_ccm_uart_hz(void);
 uint32_t imx_ccm_ahb_hz(void);
+#ifdef __rtems__
+uint32_t imx_ccm_ecspi_hz(void);
+#endif /* __rtems__ */
 
 #ifndef __rtems__
 void imx_ccm_usb_enable(device_t _usbdev);