riscv: Do not use fortify in early code

Early code designates the code executed when the MMU is not yet enabled,
and this comes with some limitations (see
Documentation/arch/riscv/boot.rst, section "Pre-MMU execution").

FORTIFY_SOURCE must be disabled then since it can trigger kernel panics
as reported in [1].

Reported-by: Jason Montleon <jmontleo@redhat.com>
Closes: https://lore.kernel.org/linux-riscv/CAJD_bPJes4QhmXY5f63GHV9B9HFkSCoaZjk-qCT2NGS7Q9HODg@mail.gmail.com/

 [1]
Fixes: a35707c3 ("riscv: add memory-type errata for T-Head")
Fixes: 26e7aacb ("riscv: Allow to downgrade paging mode from the command line")
Cc: stable@vger.kernel.org
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20241009072749.45006-1-alexghiti@rivosinc.com


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