[flash] l1: use "proper" bit definition naming.

Part 1 of 4: updated l1 to use flash_<reg>_bit instead of just flash_bit
[flash] f1: use "proper" bit definition naming.

Part 2 of 4: updated f1 to use flash_<reg>_bit instead of just
flash_bit
[flash] f2: use "proper" bit definition naming.

Part 3 of 4: updated f2 to use flash_<reg>_bit instead of just
flash_bit
[flash] f4: use "proper" bit definition naming.

Part 4 of 4: updated f4 to use flash_<reg>_bit instead of just
flash_bit