MIPS: ath79: Allow using ath79_ddr_wb_flush() from drivers

MIPS: ath79: Allow using ath79_ddr_wb_flush() from drivers

Move the declaration of ath79_ddr_wb_flush() to asm/mach-ath79/ath79.h
to allow using it from drivers. This is needed to move the CPU IRQ
driver to drivers/irqchip.

Signed-off-by: Alban Bedel <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Jason Cooper <[email protected]>
Cc: Marc Zyngier <[email protected]>
Cc: Alexander Couzens <[email protected]>
Cc: Joel Porquet <[email protected]>
Cc: Andrew Bresticker <[email protected]>
Cc: [email protected]
Cc: [email protected]
Patchwork: https://patchwork.linux-mips.org/patch/11502/
Signed-off-by: Ralf Baechle <[email protected]>