Revert "bcm53xx: use uncompressed zImages"

Revert "bcm53xx: use uncompressed zImages"

This reverts commit b3be33f135f447d56ef9a5461e7e675d5cc35730.

CFE is known to fail in some non-standard cases, e.g. when using kernel
or format different that what was tested by Broadcom. This kernel change
triggered some problem with booting OpenWrt kernel stored in Seama.

As long as Seama checksum was covering enough data, it was working fine.
We need to change it however, because calculating MD5 over part of UBI
containing SquashFS is unsafe. UBI may move PEBs depending on flash
wearing level which would break CFE booting the image.

For some reason this kernel change was breaking CFE. Calculating MD5
over 0x47ffc0 B data or less (there is 0x40 B long header) was stopping
booting process at:
Starting program at 0x00008000

As our kernel is usually 0x3fffc0 B it was affected by this problem.

Reverting this change fixes sysupgrade (which already uses kernel size
for MD5 calculation) and will allow us to adjust "fixseama" command call
on the first boot.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>