char: misc: Increase the maximum number of dynamic misc devices to 1048448

char: misc: Increase the maximum number of dynamic misc devices to 1048448

On AmpereOne, 128 dynamic misc devices is not enough for the per-cpu
coresight_tmc devices.  Switch the dynamic minors allocator to an ida and
add logic to allocate in the ranges [0..127] and [256..1048575], leaving
[128..255] for static misc devices.  Dynamic allocations start from 127
growing downwards and then increasing from 256, so device numbering for the
first 128 devices remain the same as before.

Signed-off-by: D Scott Phillips <scott@os.amperecomputing.com>
Link: https://lore.kernel.org/r/20221114212212.9279-1-scott@os.amperecomputing.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>