arm: spear: Some changes / updates to the x600 config header

arm: spear: Some changes / updates to the x600 config header

This patch brings the following changes to the x600 board support:

- Add USB EHCI support
- Add VFAT support for USB key file access
- Increase malloc size (for UBI / UBIFS usage)
- Enable Thumb mode to save some image space
- Remove unreferenced CONFIG_STACKSIZE
- Remove unreferenced CONFIG_SPL_NO_PRINTF

Signed-off-by: Stefan Roese <sr@denx.de>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Vipin Kumar <vk.vipin@gmail.com>