sdcard: direct I/O file access write buffer alignment

It is not enough to align the read buffer only, because
consequent writes might still fail with EINVAL. The write
buffer should be also aligned according to the write(2)
manual page.

Change-Id: I7547dec5208732c56f4466c1b0c88f36dabacf5b
Handle FUSE_FSYNCDIR as FUSE_FSYNC

There have been issues with sdcard data corruption even after
successfully calling fsync for /sdcard. This is caused by
the sdcard daemon doing nothing in this case.

Change-Id: I48149ceabdac79ac535b35c2598bb1fbb5410883