powerpc/32: Avoid #ifdef nested with FTR_SECTION on booke syscall entry

On booke, SYSCALL_ENTRY macro nests an FTR_SECTION with a #ifdef
CONFIG_KVM_BOOKE_HV.

Duplicate the single instruction alternative to avoid nesting.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/33db61d5f85146262dbe26648f8f87eca3cae393.1622818435.git.christophe.leroy@csgroup.eu