target/ppc: Fix build warnings when building with 'disable-tcg'

target/ppc: Fix build warnings when building with 'disable-tcg'

Kowshik reported that building qemu with GCC 12.2.1 for 'ppc64-softmmu'
target is failing due to following build warnings:

<snip>
 ../target/ppc/cpu_init.c:7018:13: error: 'ppc_restore_state_to_opc' defined but not used [-Werror=unused-function]
 7018 | static void ppc_restore_state_to_opc(CPUState *cs,
<snip>

Fix this by wrapping these function definitions in 'ifdef CONFIG_TCG' so that
they are only defined if qemu is compiled with '--enable-tcg'

Reported-by: Kowshik Jois B S <kowsjois@linux.ibm.com>
Fixes: 61bd1d2942 ("target/ppc: Convert to tcg_ops restore_state_to_opc")
Fixes: 670f1da374 ("target/ppc: Implement hashst and hashchk")
Fixes: 53ae2aeb94 ("target/ppc: Implement hashstp and hashchkp")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1319
Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Kowshik Jois B S <kowsjois@linux.vnet.ibm.com>
Message-Id: <20221116131743.658708-1-vaibhav@linux.ibm.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>