Add emmc_optimized flag

Bug: 144046242
Test: atest libfscrypt_unit_test
Test: Change fstab on Cuttlefish with patched kernel, check dir policy
Cherry-Picked-From: 476ce0a30615c1249969bedba0f1fb084d8ef193
Merged-In: I362f9a55fa28bb25afe992c8b0bae48546fc9ab0
Change-Id: I362f9a55fa28bb25afe992c8b0bae48546fc9ab0
3 files changed