This patch adds indexed variants of the floating-point fused multiply-add/subtract long to/from accumulator instructions.
FMLAL <Vd>.<Ta>, <Vn>.<Tb>, <Vm>.H[<index>]
FMLAL2 <Vd>.<Ta>, <Vn>.<Tb>, <Vm>.H[<index>]
FMLSL <Vd>.<Ta>, <Vn>.<Tb>, <Vm>.H[<index>]
FMLSL2 <Vd>.<Ta>, <Vn>.<Tb>, <Vm>.H[<index>]
Issue: #2626