vold: Fix build for minivold and general cleanup

Change-Id: Ibc450dd86b77a0c4a25de08b2f07dfb9b2c70871
vold: Fix uses of board flags

Put LOCAL_CFLAGS += AFTER LOCAL_CFLAGS := ..
Else all flags will be removed/ignored ..
That fixes MAX_PARTITIONS flag usage ..

Change-Id: I96854b7de1eae6a235e8d31f7a9364a680b4f0b6
vold: Support unmount <path> detach

This is to be used primarily (exclusively?) in recovery.  In prior
versions, the local file was copied to tmpfs so that everything could
be unmounted cleanly.  But the current version uses the local file
in-place due to constraints with low memory devices.  This prevents
the filesystem that holds the local file from being unmounted in the
normal way.  So in order to avoid leaking a mount, the filesystem that
holds the local file must be unmounted with the detach flag.

Change-Id: I17716f131225b54ca3bc9d2215a45d22d1841137
vold: fix build.

Change-Id: If19cb8ccdbb8466e92480136b0d2a14d59847a2e
vold: Mount ext4/f2fs sdcards with sdcard_posix context

Change-Id: I05d9b57cc28ffd1f8deb8148d81c7f6fad0aa8db