arch: riscv: add Kconfig option for imprecise FPU state tracking

According to the RISC-V Instruction Set Manual: Volume II, Version 20240411
(Section 3.1.6.6), some implementations may choose to track the dirtiness
of the floating-point register state imprecisely by reporting the state to
be dirty even when it has not been modified. This option reflects that.

Also add a filter in `tests/arch/riscv/fpu_sharing/` based on imprecise
FPU state tracking

Signed-off-by: Jakub Wasilewski <jwasilewski@internships.antmicro.com>
Signed-off-by: Filip Kokosinski <fkokosinski@antmicro.com>