ppc: Remove T2081QDS board and ARCH_T2081 support

This board has not been converted to CONFIG_DM_MMC by the deadline.
Remove it.  It is also the only ARCH_T2081 board so remove that support
as well.

Cc: Shengzhou Liu <Shengzhou.Liu@nxp.com>
Cc: Ruchika Gupta <ruchika.gupta@nxp.com>
Signed-off-by: Tom Rini <trini@konsulko.com>