This PR implements the EVM gas price syscall API method. Currently this
is a compile time constant in revive, but in the EVM it is an opcode.
Thus we should provide an opcode for this in the pallet.

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Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>
Signed-off-by: xermicus <cyrill@parity.io>
Co-authored-by: command-bot <>