net: macb: sync header definitions as taken from Linux

Few registers and bits were added by Cadence and
they were not updated in the headers.
Take the latest definitions as defined in Linux
header (5.1) that also includes some comments
about existing registers.

One register was improperly named (UR), fix that.

Signed-off-by: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
Tested-by: Anup Patel <anup.patel@wdc.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>