package/freerdp: add options to enable/disable server and/or client

Building the client or the server requires an X.Org stack.

Since freerdp can also be used for weston (wayland-based, hence no X.Org
stack), we may want to disable the client and server.

Conversely, even with an X.Org stack, we may want to enable either or
none if we're just interested in the library.

Add two options, one to enable the server, the other the client; the
client option defaults to 'Y' so that a previous .config can be re-used
as-is, and exhibit the same behaviour as before; the server option
defaults to 'N' as we were not ever building the server so far.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Samuel Martin <s.martin49@gmail.com>
Reviewed-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>