RISC-V: pi: Force hidden visibility for all symbol references

Eliminate all GOT entries in the .pi section, by forcing hidden
visibility for all symbol references, which informs the compiler that
such references will be resolved at link time without the need for
allocating GOT entries.

Include linux/hidden.h in Makefile, like arm64, for the
hidden visibility attribute.

Signed-off-by: Jesse Taube <jesse@rivosinc.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240709173937.510084-2-jesse@rivosinc.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>