package.bbclass: Create empty key/value if not there for shlib_provider

package.bbclass: Create empty key/value if not there for shlib_provider

When we use ASSUME_SHLIBS,e.g.

ASSUME_SHLIBS = "libEGL.so.1:libegl-implementation"

then we end up with errors like below when using shlibs2 (dizzy+)

File: 'package_do_shlibs', lineno: 216, function: package_do_shlibs
     0212:            dep_pkg = dep_pkg.rsplit("_", 1)
     0213:            if len(dep_pkg) == 2:
     0214:                lib_ver = dep_pkg[1]
     0215:            dep_pkg = dep_pkg[0]
 *** 0216:            shlib_provider[l][libdir] = (dep_pkg, lib_ver)
     0217:
     0218:    libsearchpath = [d.getVar('libdir', True),
d.getVar('base_libdir', True)]
     0219:
     0220:    for pkg in packages.split():
Exception: KeyError: 'libEGL.so.1'

This is because the entry which is being populated does not exist
so lets create it if its not already there.

Change-Id: I9e292c5439e5d1e01ea48341334507aacc3784ae
Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>