decompress: fix new decompressor for PIC

The ARM kernel decompressor wants to be able to relocate r/w data
independently from the rest of the image, and we do this by ensuring that
r/w data has global visibility.  Define STATIC_RW_DATA to be empty to
achieve this.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Alain Knaff <alain@knaff.lu>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>