bootm: Align cache flush end address correctly

bootm: Align cache flush end address correctly

Flushing part of the cache should be done on cache boundaries. Trying to
flush part of a cache line is not supported and the request may be ignored
or print warnings.

Adjust the bootm code to align the end address to prevent this problem.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>
Tested-on: smartweb, corvus, taurus, axm
Tested-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Andreas Bießmann <andreas@biessmann.org>