30.2.1. ARM B instruction
Unconditional branch.
Example: userland/arch/arm/b.S
The encoding stores PC offsets in 24 bits. The destination must be a multiple of 4, which is easy since all instructions are 4 bytes.
This allows for 26 bit long jumps, which is 64 MiB.
TODO: what to do if we want to jump longer than that?