riscv: fpu: switch has_fpu() to riscv_has_extension_likely()

Switch has_fpu() from static branch to the new helper
riscv_has_extension_likely().

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230128172856.3814-7-jszhang@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>