Add -mfpu=neon-vfpv4

This enables user to architecturally specify ARMv7A + VFPv4 + NEON.

Change-Id: I779b01fef5c47e5e4ac702ae24ed2f76a0e4c63f
Add additional arguments for -mfpu options

Add neon-vfpv3 to allow specifying both at the same time. This is not an
option that GCC supports, but follows the same track and should be
non-controversial.

Change-Id: Id9ec157c835937d7d11ad0f49dbe5171fac17658