Provide a conversion function from utf8 to utf16.

Add missing #include <linux/types.h> in include/charset.h.
Remove superfluous #include <common.h> in lib/charset.c.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>

The constant MAX_UTF8_PER_UTF16 is used to calculate
required memory when converting from UTF-16 to UTF-8.
If this constant is too big we waste memory.

A code point encoded by one UTF-16 symbol is converted to a
maximum of three UTF-8 symbols, e.g.

0xffff could be encoded as 0xef 0xbf 0xbf.
The first byte carries four bits, the second and third byte
carry six bits each.

A code point encoded by two UTF-16 symbols is converted to four
UTF-8 symbols.

So in this case we need a maximum of two UTF-8 symbols per
UTF-16 symbol.

As the overall maximum is three UTF-8 symobls per UTF-16 symbol
we need MAX_UTF8_PER_UTF16 = 3.

Fixes: 78178bb0c9d lib: add some utf16 handling helpers
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>

We'll eventually want these in a few places in efi_loader, and also
vsprintf.

Signed-off-by: Rob Clark <robdclark@gmail.com>