arm: socfpga: clock: Add missing stubs into board file

Add some stub defines, which are used by the clock code, but are
missing from the auto-generated header file for the SoCFPGA family.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chin Liang See <clsee@altera.com>
Cc: Dinh Nguyen <dinguyen@altera.com>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Tom Rini <trini@ti.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Pavel Machek <pavel@denx.de>
Acked-by: Dinh Nguyen <dinguyen@opensource.altera.com>
Acked-by: Pavel Machek <pavel@denx.de>