add new board bananapim7

[amazingfate]

Description

bananapim7 and armsom-sige7 are the same board. This pr will simplely add a new board with a different name.
legacy and vendor kernel dts are added in armbian/linux-rockchip#160 and armbian/linux-rockchip#161

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also note any relevant details for your test configuration.

• ./compile.sh BOARD=bananapim7 BRANCH=edge BUILD_DESKTOP=no BUILD_MINIMAL=no COMPRESS_OUTPUTIMAGE=sha,gpg,xz DEB_COMPRESS=xz KERNEL_CONFIGURE=no RELEASE=bookworm
• ./compile.sh kernel BOARD=bananapim7 BRANCH=legacy DEB_COMPRESS=xz KERNEL_CONFIGURE=no
• ./compile.sh kernel BOARD=bananapim7 BRANCH=vendor DEB_COMPRESS=xz KERNEL_CONFIGURE=no

Checklist:

Please delete options that are not relevant.

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

[rpardini]

Looks fine. It will not conflict with #6471 but I'd love to merge that first since there's renames / rewrites in there