riscv: Remove ld.lld version checks from many TOOLCHAIN_HAS configs

riscv: Remove ld.lld version checks from many TOOLCHAIN_HAS configs

Now that the minimum supported version of LLVM for building the kernel
has been bumped to 15.0.0, several ld.lld version checks become
tautological, as they are always true. Replace them with a simple
CONFIG_LD_IS_LLD check.

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250821-bump-min-llvm-ver-15-v2-9-635f3294e5f0@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>