Qemu-pipe: refactor qemu_pipe.h into libqemu_pipe

Traditionally, qemu_pipe has both the declaration and implentation of each
function in one header file--qemu_pipe.h, and it is getting incovenient to
maintain.

This CL separates the implementation of functions from the header file,
and makes qemu_pipe a static library for other modules to link to.

Note that the interface and implementation of qemu_pipe are kept unchanged,
and future CLs will enhance the implementation to make it more reliable and
more compatible with old and new API levels.

Following projects are affected by this refactoring, and they are modified
accordingly:

hardware/ril/reference-ril

Change-Id: I541ecbf0cc7eadeef9d4e37ffd9ca7bfcc5c94c0
(cherry picked from aosp 294d44be)