ramips: mt7620: use OKLI loader with Jboot devices

ramips: mt7620: use OKLI loader with Jboot devices

Jboot devices have problem with >2MB kernelsize. The only way to avoid
this problem is use small loader.

This patch switch all mt7620 Jboot devices to lzma OKLI loader.

Suggested-by: Szabolcs Hubai <szab.hu@gmail.com>
Co-authored-by: Michael Pratt <mcpratt@pm.me>
Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>