arm64: Properly clear BSS

arm64: Properly clear BSS

Brock reports a breakage on an RK3568 SoC. His patch is
correct but he never followed up on the requested changes.

We currently use ldr to calculate the address of __bss_start and
__bss_end. However the absolute addresses of the literal pool are never
relocated and we end up clearing the wrong memory section. Use
PC-relative addressing instead.

Link: https://lore.kernel.org/u-boot/zfknlzcemnnaka5w2er5wjwefwoidrpndc4gjhx6d5xr6nlcjr@pasfayjiutii/
Suggested-by: brock_zheng <yzheng@techyauld.com>
Reported-by: brock_zheng <yzheng@techyauld.com>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>