arm: socfpga: Add command to control HPS-FPGA bridges

Add command to enable and disable the bridges between HPS and FPGA.

This patch does have a checkpatch issue with the assembler portion,
checkpatch correctly complains that there should be no whitespace
before quoted newline. I do not agree that fixing this specific
checkpatch issue will improve the readability, thus this one is not
addressed.

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