add 'unzip' command to u-boot commandline

[PATCH] add new 'unzip' command to u-boot commandline

common/cmd_mem.c: new command "unzip srcaddr dstaddr [dstsize]" to unzip from
memory to memory, and option CONFIG_CMD_UNZIP to enable it

Signed-off-by: Werner Almesberger <werner@openmoko.org>
Signed-off-by: Harald Welte <laforge@openmoko.org>