ARM: dts: msm: Update Graphics SMMU CB allotment

GFX can use 2 CBs for their non-secure use-cases. Also,
update the CB allotment and reserve CB0 for Stage-2
programming.

Change-Id: Ibbcd26afbd50fe760c4052d0e11b4429aacf3e64
Signed-off-by: Chintan Pandya <cpandya@codeaurora.org>
Signed-off-by: Susheel Khiani <skhiani@codeaurora.org>