md: add md_submit_discard_bio() for submitting discard bio

md: add md_submit_discard_bio() for submitting discard bio

BugLink: https://bugs.launchpad.net/bugs/1896578
Move these logic from raid0.c to md.c, so that we can also use it in
raid10.c.

Reviewed-by: Coly Li <colyli@suse.de>
Reviewed-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Tested-by: Adrian Huang <ahuang12@lenovo.com>
Signed-off-by: Xiao Ni <xni@redhat.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
(cherry picked from commit cf78408f937a67f59f5e90ee8e6cadeed7c128a8)
Signed-off-by: Matthew Ruffell <matthew.ruffell@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>