msm: kgsl: Use one define for max priority levels

Don't redefine the macro since that could result in inconsistent
data if one of them changes and the isn't updated.

CRs-Fixed: 971159
Change-Id: I57ab3113fbdd82c70cba1c79f4b996cea09a8739
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>