This patch adds definitions to support user space device mappings
that allows devices like frame buffer to be accessible from user
space in kernel mode.
The are mainly two changes:
- in `mm/`:
added vm_map_region(), vm_unmap_region() for drivers to do
device mapping easily.
- in `arch/`:
extended ARCH_SHM_NPAGES as user-space mapping region size.
decoupled ARCH_SHM_MAXREGIONS from region size calculations and
limit its usage only for SysV shm purposes.
Signed-off-by: Yanfeng Liu <yfliu2008@qq.com>
3822d88669