Add support for lzma compressed uImage.

Support for gzip was already available but could not be enabled because
we were missing CONFIG_HAVE_KERNEL_GZIP in arch/arc/Kconfig.
Signed-off-by: Daniel Mentz <danielmentz@google.com>
Cc: linux-snps-arc@lists.infradead.org
Cc: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>