ctype: align size of category bit fields to small targets needs

ctype: align size of category bit fields to small targets needs

E.g. arm ABI requires -fshort-enums for bare-metal toolchains.
Given there are only 29 category enums, the compiler chooses an
8 bit enum type, so a size of 11 bits for the bitfield leads to
a compile time error:

  error: width of 'cat' exceeds its type
    enum category cat: 11;
                  ^~~

Fix this by aligning the size of the category members to byte
borders.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>