arm: socfpga: reset: Add function to reset FPGA bridges

arm: socfpga: reset: Add function to reset FPGA bridges

Add function to enable and disable FPGA bridges. This code is used
by the FPGA manager to disable the bridges before programming the
FPGA and will later be also used by the initialization code for the
chip to put the chip into well defined state during startup.

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: Pavel Machek <pavel@denx.de>