RISC-V: add f & d extension validation checks

RISC-V: add f & d extension validation checks

Using Clement's new validation callbacks, support checking that
dependencies have been satisfied for the floating point extensions.

The check for "d" might be slightly confusingly shorter than that of "f",
despite "d" depending on "f". This is because the requirement that a
hart supporting double precision must also support single precision,
should be validated by dt-bindings etc, not the kernel but lack of
support for single precision only is a limitation of the kernel.

Tested-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Clément Léger <cleger@rivosinc.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250312-reptile-platinum-62ee0f444a32@spud
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>