beagle regulator updates

For Beagle, link two regulators to the MMC-1 host adapter.

Note:  when MMC1 is used in 8 bit mode (e.g. for an MMCplus card)
DAT4..DAT7 I/O uses a separate supply (VSIM).  But MMC_BUS_WIDTH_8
support isn't yet merged into the MMC framework.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>