RISC-V: add vector extension validation checks

Using Clement's new validation callbacks, support checking that
dependencies have been satisfied for the vector extensions. From the
kernel's perfective, it's not required to differentiate between the
conditions for all the various vector subsets - it's the firmware's job
to not report impossible combinations. Instead, the kernel only has to
check that the correct config options are enabled and to enforce its
requirement of the d extension being present for FPU support.

Since vector will now be disabled proactively, there's no need to clear
the bit in elf_hwcap in riscv_fill_hwcap() any longer.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250312-eclair-affluent-55b098c3602b@spud


Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>