target/ppc: implement cdtbcd

target/ppc: implement cdtbcd

Implements the Convert Declets To Binary Coded Decimal instruction.
Since libdecnumber doesn't expose the methods for direct conversion
(decDigitsFromDPD, DPD2BCD, etc), a positive decimal32 with zero
exponent is used as an intermediate value to convert the declets.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Signed-off-by: Víctor Colombo <victor.colombo@eldorado.org.br>
Message-Id: <20220629162904.105060-12-victor.colombo@eldorado.org.br>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>