MIPS: compressed: Use correct instruction for 64 bit code

The code clearing BSS already use macro or use correct instruction
depending if the CPU is 32 bits or 64 bits. However, a few
instructions remained 32 bits only.

By using the accurate MACRO, it is now possible to deal with memory
address beyond 32 bits. As a side effect, when using 64bits processor,
it also divides the loop number needed to clear the BSS by 2.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>