Fix Softserial

[haslinghuis]

Also adds flash support to BETAFPVF4SX1280 board.

[blckmn]

AUTOMERGE: (FAIL)

• github identifies PR as mergeable -> FAIL
• assigned to a milestone -> PASS
• cooling off period lapsed -> PASS
• commit count less or equal to three -> PASS
• Don't merge label NOT found -> PASS
• at least one RN: label found -> PASS
• Tested label found -> FAIL
• assigned to an approver -> PASS
• approver count at least three -> FAIL

[nerdCopter]

flashed BETAFPVF4SX1280 and it saw resource SERIAL_TX 11 A08 proper.
mine does not have flash to test.

[haslinghuis]

Have two, one is a special build from betafpv with added flash. @asizon also has this very limited edition.
Put back two resources as they don't interfere

[ctzsnooze]

Thanks, Mark @haslinghuis

[github-actions]

Do you want to test this code? Here you have an automated build:
Assets
WARNING: It may be unstable. Use only for testing! See: https://www.youtube.com/watch?v=I1uN9CN30gw for instructions for unified targets!