target/ppc: Restore [H]DEXCR to 64-bits

The DEXCR emulation was recently changed to a 32-bit register, possibly
because it does have a 32-bit read-only view. It is a full 64-bit
SPR though, so use the corresponding 64-bit write functions.

Fixes: fbda88f ("target/ppc: Fix width of some 32-bit SPRs")
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

target/ppc/cpu_init.c

@@ -5820,7 +5820,7 @@ static void register_power10_dexcr_sprs(CPUPPCState *env)
 {
     spr_register(env, SPR_DEXCR, "DEXCR",
             SPR_NOACCESS, SPR_NOACCESS,
-            &spr_read_generic, &spr_write_generic32,
+            &spr_read_generic, &spr_write_generic,
             0);
 
     spr_register(env, SPR_UDEXCR, "UDEXCR",
@@ -5831,7 +5831,7 @@ static void register_power10_dexcr_sprs(CPUPPCState *env)
     spr_register_hv(env, SPR_HDEXCR, "HDEXCR",
             SPR_NOACCESS, SPR_NOACCESS,
             SPR_NOACCESS, SPR_NOACCESS,
-            &spr_read_generic, &spr_write_generic32,
+            &spr_read_generic, &spr_write_generic,
             0);
 
     spr_register(env, SPR_UHDEXCR, "UHDEXCR",