target/ppc: Implement Vector Insert from GPR using GPR index insns

target/ppc: Implement Vector Insert from GPR using GPR index insns

Implements the following PowerISA v3.1 instructions:
vinsblx: Vector Insert Byte from GPR using GPR-specified Left-Index
vinshlx: Vector Insert Halfword from GPR using GPR-specified Left-Index
vinswlx: Vector Insert Word from GPR using GPR-specified Left-Index
vinsdlx: Vector Insert Doubleword from GPR using GPR-specified
         Left-Index
vinsbrx: Vector Insert Byte from GPR using GPR-specified Right-Index
vinshrx: Vector Insert Halfword from GPR using GPR-specified
         Right-Index
vinswrx: Vector Insert Word from GPR using GPR-specified Right-Index
vinsdrx: Vector Insert Doubleword from GPR using GPR-specified
         Right-Index

The helpers and do_vinsx receive i64 to allow code sharing with the
future implementation of Vector Insert from VSR using GPR Index.

Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Message-Id: <20211104123719.323713-6-matheus.ferst@eldorado.org.br>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>