30.4.3.2. ARMv8 aarch64 movk instruction
Fill a 64 bit register with 4 16-bit instructions one at a time.
Similar to ARM movw and movt instructions in v7.
Example: userland/arch/aarch64/movk.S
Bibliography: https://stackoverflow.com/questions/27938768/moving-a-32-bit-constant-in-arm-arch64-register