mtd: brcmnand: clean up flash cache for parameter pages

The read_byte() handling for accessing the flash cache has some awkward
swapping being done in the read_byte() function. Let's just make this a
byte array, and do the swapping with the word-level macros during the
initial buffer copy.

This is just a refactoring patch, with no (intended) functional change.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Clay McClure <clay@daemons.net>
Cc: Ray Jui <rjui@broadcom.com>
Cc: Scott Branden <sbranden@broadcom.com>
Cc: <bcm-kernel-feedback-list@broadcom.com>
Tested-by: Clay McClure <clay@daemons.net>