New: Add A extension decoding #290

Job	Run time
Synthesis	4m 7s
Privilege-Security-Testsuite	4m 5s
WBA-Testsuite	6m 35s
Lint	15s
C-Testsuite	2m 25s
SV-Testsuite	16s
RISCV-Compliance	18m 29s
	36m 12s

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