ath79: lzma-loader: expose LZMA_TEXT_ADDRESS configuration again

ath79: lzma-loader: expose LZMA_TEXT_ADDRESS configuration again

initramfs for some devices grew so big, that it can't be loaded within
the previous 32MB RAM limit. Make the LZMA_TEXT_ADDRESS configurable
per-target once again, to fix it for bigger devices, while maintaining
compatibility with previous ones.

Signed-off-by: Lech Perczak <lech.perczak@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/17616
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit 6720958659d226e71dca49657202e0502bb059bd)