dm-verity: allow REED_SOLOMON to be 'm' if DM_VERITY is 'm'

dm-verity: allow REED_SOLOMON to be 'm' if DM_VERITY is 'm'

The dm-verity kconfig options make the common mistake of selecting a
dependency from a bool "sub-option" rather than the main tristate
option.  This unnecessarily forces the dependency to built-in ('y').

Fix this by moving the selections of REED_SOLOMON and REED_SOLOMON_DEC8
into DM_VERITY, conditional on DM_VERITY_FEC.

This allows REED_SOLOMON to be 'm' if DM_VERITY is 'm'.

Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>