ramoops: use the platform data structure instead of module params

As each board and system has different memory for ramoops.  It's better to
define the platform data instead of module params.

[akpm@linux-foundation.org: fix ramoops_remove() return type]
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Marco Stornelli <marco.stornelli@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>