vold: allow override of MAX_PARTITIONS for devices with > 4 partitions

Change-Id: Iaa6ebe57710ffe93156e3a9e47739ad771bd314b
DirectVolume: handle discs with multiple major numbers

CFlag: BOARD_VOLD_DISC_HAS_MULTIPLE_MAJORS

Allows Direct Volume to handle discs with multiple major numbers.
Needed on Samsung Galaxy S II and variants.

For example:
mmcblk0p1 - 179:0
mmcblk0p2 - 179:1
mmcblk0p3 - 179:2
mmcblk0p4 - 256:0
mmcblk0p5 - 256:1

Change-Id: I633ac882a721cde25f0df779b4028efa6be15750
Reintroduce BOARD_VOLD_EMMC_SHARES_DEV_MAJOR

Code taken from CM7's vold

Change-Id: Iaa6ebe57710ffe93156e3a9e47739ad771bd314b