MIPS: vmlinux.lds.S: explicitly catch .rel.dyn symbols

MIPS: vmlinux.lds.S: explicitly catch .rel.dyn symbols

According to linker warnings, both GCC and LLVM generate '.rel.dyn'
symbols:

mips-alpine-linux-musl-ld: warning: orphan section `.rel.dyn'
from `init/main.o' being placed in section `.rel.dyn'

Link-time assertion shows that this section is sometimes empty,
sometimes not, depending on machine bitness and the compiler [0]:

  LD      .tmp_vmlinux.kallsyms1
mips64-linux-gnu-ld: Unexpected run-time relocations (.rel) detected!

Just use the ARM64 approach and declare it in vmlinux.lds.S closer
to __init_end.

[0] https://lore.kernel.org/linux-mips/20210109111259.GA4213@alpha.franken.de

Reported-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>