rhine: bt: disable clock-sharing

not used in GPe or stock rom, no idea if is really useful

Change-Id: Iedfe54afbff3052e6b77baa5c15577dd0bce1e5c
rhine: set VM_MAX_READAHEAD to 512K

Change-Id: I49e23923d8d11b1979cd0c501702d48916056047