[SPE] Minor event_filter implementation cleanup

Description

We have some magic numbers used in implementation of SPE filter event_filter. See below:

windowsperf (master)$ git grep 0x8AA
wperf-driver/spe.cpp:            _WriteStatusReg(PMSEVFR_EL1, context->event_filter & 0x8AA);
wperf-driver/spe.cpp:            if (context->event_filter & 0x8AA)
wperf-test/wperf-test-parsers.cpp:                      test(L"2218", 0x8AA);
wperf-test/wperf-test-parsers.cpp:                      test(L"0x8AA", 0x8AA);
wperf-test/wperf-test-parsers.cpp:                      test(L"0x00000000000008AA", 0x8AA);
wperf/SPE.md:- `event_filter=<n>` - collect only events that match all of the the specified filters. This value is written to `PMSEVFR`. Only bits 1, 3, 5, 7, and 11 (mask 0x8AA) may be used.
wperf/spe_device.h:            {L"event_filter",   {0, 0x8AA}},

I think when I search for binary counterpart of 0x8AA I can find:

$ python
>>> bin(0x8aa)
'0b100010101010'

$ git grep 0b100010101010
wperf/parsers.cpp:476:                constexpr uint16_t VALID_BITS = 0b100010101010;

Definition of done

Simple refactoring to remove magic number 0x8AA and its binary counterpart from the core.
Please drag these values under one consistent const / macro etc.
- One source of this const should propagate in the code and unit test of wperf as well.