target/ppc: introduce do_ea_calc

target/ppc: introduce do_ea_calc

The do_ea_calc function will calculate the effective address(EA)
according to PowerIsa 3.1. With that, it was replaced part of
do_ldst() that calculates the EA by this new function.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Fernando Eckhardt Valle (pherde) <phervalle@gmail.com>
Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Message-Id: <20211029202424.175401-2-matheus.ferst@eldorado.org.br>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>