Some devices use mkbootimg with weird args for which fastboot
only a hardcoded value.
Now fastboot recognizes those args.
Made handling of global vars more consistent.
Bug: 8341331
Change-Id: Ic09f148ccd0249f49935fdc63e517cf8ab2229bc
Add the --base flag to mkbootimg and -b flag to fastboot, to allow
the default kernel base address (0x10000000) to be changed.
Signed-off-by: Brian Swetland <swetland@google.com>