kernel: add kcompat_sys_{f,}statfs64()

kernel: add kcompat_sys_{f,}statfs64()

Using this helper allows us to avoid the in-kernel calls to the
compat_sys_{f,}statfs64() sycalls, as are necessary for parameter
mangling in arm64's compat handling.

Following the example of ksys_* functions, kcompat_sys_* functions are
intended to be a drop-in replacement for their compat_sys_*
counterparts, with the same calling convention.

This is necessary to enable conversion of arm64's syscall handling to
use pt_regs wrappers.

Signed-off-by: Mark Rutland <[email protected]>
Reviewed-by: Dominik Brodowski <[email protected]>
Cc: Al Viro <[email protected]>
Cc: [email protected]
Signed-off-by: Will Deacon <[email protected]>