fb: JZ4770: Fill in (lack of) alpha in 16 bpp in var struct

Now the etna_viv demo applications no longer reject 16 bpp as an
unsupported pixel format.
Revert "regmap: regcache-flat: Implemented sync operation"

This reverts commit 762d66a552232706376787cd9da52bd12189aeea.

This is going to be solved in a different way.
regmap: Implemented default cache sync operation

This can be used for cache types for which syncing values one by one is
equally efficient as syncing a range, such as the flat cache.