uboot-phytec

add CONFIG_SPI_IDLE_VAL for cf_spi.c to allow use of spi_mmc

This patch adds CONFIG_SPI_IDLE_VAL to cf_spi.c
The default setting is 0x0 to behave same as current version, in case
CONFIG_SPI_MMC is set, the value is set to 0xFFFF (all ones). In either
case, the value can be overwritten by board configuration.

Signed-off-by: Wolfgang Wegner <w.wegner@astro-kom.de>
Signed-off-by: Andy Fleming <afleming@freescale.com>