riscv: Improve flush_tlb_kernel_range()

riscv: Improve flush_tlb_kernel_range()

This function used to simply flush the whole tlb of all harts, be more
subtile and try to only flush the range.

The problem is that we can only use PAGE_SIZE as stride since we don't know
the size of the underlying mapping and then this function will be improved
only if the size of the region to flush is < threshold * PAGE_SIZE.

Signed-off-by: Alexandre Ghiti <[email protected]>
Reviewed-by: Andrew Jones <[email protected]>
Tested-by: Lad Prabhakar <[email protected]> # On RZ/Five SMARC
Reviewed-by: Samuel Holland <[email protected]>
Tested-by: Samuel Holland <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>