utf8data.h_shipped has a large database table which is an auto-generated
decodification trie for the unicode normalization functions.
We can avoid carrying this large table in the kernel unless it is required
by the filesystem during boot process.

Hence, make UTF-8 encoding loadable by converting it into a module and
also add built-in UTF-8 support option for compiling it into the
kernel whenever required by the filesystem.

Modify the file called unicode-core which will act as a layer for
unicode subsystem. It will be responsible for loading the UTF-8 module
and accessing it's functions.

Currently, only UTF-8 encoding is supported but if any other encodings
are supported in future then the layer file would be responsible for
loading the desired encoding module.

Also, indirect calls using function pointers are slow, use static calls to
avoid overhead caused in case of repeated indirect calls. Static calls
improves the performance by directly calling the functions as opposed to
indirect calls.

Signed-off-by: Shreeya Patel <shreeya.patel@collabora.com>