lisa.trace: Add __cpu to HRTxtTraceParser.HEADER_REGEX
lisa.trace: Add __cpu to HRTxtTraceParser.HEADER_REGEX

Add missing group for __cpu to parse the CPU common field of each event.

ARM-software/lisa,credp/lisa,ARM-software/lisa,ARM-software/lisa,credp/lisa,credp/lisa,credp/lisa,ARM-software/lisa