recovery: replacing fs_mgr_read_fstab() with new fs_mgr APIs

The fstab settings of early-mounted partitions (e.g., /vendor) will be in
kernel device tree. Switch to the new API to get the whole settings with
those in device tree:

    fs_mgr_read_fstab_with_dt("/etc/recovery.fstab")

The original default /fstab.{ro.hardware} might be moved to
/vendor/etc/. or /odm/etc/. Use another new API to get the default fstab
instead of using the hard-coded /fstab.{ro.hardware}. This API also
includes the settings from device tree:

    fs_mgr_read_fstab_default()

Bug: 35811655
Test: boot sailfish recovery
Change-Id: Iaa56ac7f7b4c4dfc7180c65f03e9a37b94f1de09