fs: rework f2fs

Signed-off-by: arter97 <qkrwngud825@gmail.com>
f2fs: add support for LOOKUP_CASE_INSENSITIVE

For sdcardfs' case-insensitive lookup to work properly.

Initial code by Motorola, patched by @arter97 for latest f2fs sources.

Signed-off-by: arter97 <qkrwngud825@gmail.com>