msm: mdss: enable fb_split feature for Find7

This change was originally introduced by commit c4ad2bf,
but never made it into the code we actually compile for
OPPO devices.

Since this one works fine on the Find7a, too, remove the
unnecessary ifdeffing.

Reference commit: https://github.com/TeamEOS/kernel_oppo_msm8974/commit/c4ad2bf3b683048c98f95c6c2782c17cbb1b0928

Change-Id: I05ce767f05994545e61160289ee9ff5fc8b36362