yocto-bsp: Update qemu inclusion lists

Update qemu tune definitions to match changes in main qemu machines.

[YOCTO #6482]

(From meta-yocto rev: 6c9bbe848b4134a38ffac2c1ac02f32368f55081)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/bsp/substrate/target/arch/qemu/conf/machine/{{=machine}}.conf

@@ -37,7 +37,7 @@ require conf/machine/include/qemu.inc
 require conf/machine/include/tune-arm926ejs.inc
 {{ if qemuarch == "powerpc": }}
 require conf/machine/include/qemu.inc
-require conf/machine/include/tune-ppc603e.inc
+require conf/machine/include/tune-ppc7400.inc
 {{ if qemuarch == "mips": }}
 require conf/machine/include/qemu.inc
 require conf/machine/include/tune-mips32.inc