This patch supports the EL0 and EL1 system registers used in MRS/MSR
instructions. This patch refactors the assembler code, allowing the
assembler to read system register information from the automatically
generated sysRegEnc.go file and move existing declared system registers
to the sysRegEnc.go file.

This patch adds 431 system registers, it is worth noting that the number
of special registers is initialized to less than 1024 in the list7.go file.

This CL also adds some test cases to test the newly added system registers.

The test cases are contributed by Dianhong Xu <Dianhong.Xu@arm.com>

Change-Id: Ic09a937eaaeefe82bd08b5dd726808f8ff6cebf6
Reviewed-on: https://go-review.googlesource.com/c/go/+/189577Reviewed-by: Ben Shi <powerman1st@163.com>
Run-TryBot: Ben Shi <powerman1st@163.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>