mediapc: Fix initializationError on devices without h/w codecs

When mediapc tests were run on devices without h/w avc codecs,
tests failed with initializationError.
This error was seen in static {} block when getting name of avc h/w
decoder and encoder. This code is now moved to SetUp() and an assume is
added such that test now returns ASSUMPTION_FAILURE on devices that do
not contain h/w avc codecs.

Bug: 192434578
Bug: 195673102
Test: atest CtsMediaPerformanceClassTestCases
Merged-in: Ic7649a40ef174497a58f60bb2b784651ad6aa1db
Change-Id: Ic7649a40ef174497a58f60bb2b784651ad6aa1db