The change adds support of ARM PrimeCell PL176 MPMC.

Static memory configuration of PL175 MPMC is very similar to one found
on PL172 and PL175 controllers, so it is preferred to add its support
into the existing driver. The difference is that PL176 supports up to
10 slave ports (but only 4 of them may be connected to static memory
devices), AHB master bus width cab be 64-bit wide, also NAND devices
can be interfaced.

Similar to PL175 contoller, PL176 has no write buffer enable control
in static memory configuration register, the rest of static memory
configuration bits (with exception of NAND) is the same.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Joachim Eastwood <manabian@gmail.com>