configs: apalis-tk1: Do not define CONFIG_SYS_BOOT_RAMDISK_HIGH again

CONFIG_SYS_BOOT_RAMDISK_HIGH is already defined in
arch/arm/include/asm/config.h:10:#define CONFIG_SYS_BOOT_RAMDISK_HIGH
that's why there is no reason to define it again in board file.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>