riscv: linker: lld: Handle symtab/strtab/shstrtab to fix warnings

lld will produce warnings for the symtab, strtab, and shstrtab sections
if --orphan-handling=warn is specified and there are no matching rules
in the linker script for these sections. Handle these sections when
building with lld to prevent the warnings.

Signed-off-by: Jonathon Penix <jpenix@quicinc.com>