ACPICA: OSL: Add portable file IO to improve portability

This patch adds portable file IO to generic OSL to improve the portability
of the applications.

A portable application may use different file IO interfaces than the
standard C library ones. This patch thus introduces an abstract file IO
layer into the generic OSL.

Note that this patch does not introduce users of such interfaces, further
patches should introduce users one by one carefully with build tests
performed. Lv Zheng.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>