image: Add compressed Image parsing support in booti.

Add compressed Image parsing support so that booti can parse both
flat and compressed Image to boot Linux. Currently, it is difficult
to calculate a safe address for every board where the compressed
image can be decompressed. It is also not possible to figure out the
size of the compressed file as well. Thus, user need to set two
additional environment variables kernel_comp_addr_r and filesize to
make this work.

Following compression methods are supported for now.
lzma, lzo, bzip2, gzip.

lz4 support is not added as ARM64 kernel generates a lz4 compressed
image with legacy header which U-Boot doesn't know how to parse and
decompress.

Tested on HiFive Unleashed and Qemu for RISC-V.
Tested on Qemu for ARM64.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
[trini: Fix minor rST formatting problems]
Signed-off-by: Tom Rini <trini@konsulko.com>