powerpc/32: implement fast entry for syscalls on BOOKE

This patch implements a fast entry for syscalls.

Syscalls don't have to preserve non volatile registers except LR.

This patch then implement a fast entry for syscalls, where
volatile registers get clobbered.

As this entry is dedicated to syscall it always sets MSR_EE
and warns in case MSR_EE was previously off

It also assumes that the call is always from user, system calls are
unexpected from kernel.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/entry_32.S

@@ -342,7 +342,6 @@ stack_ovf:
 	SYNC
 	RFI
 
-#ifndef CONFIG_BOOKE	/* to be removed once BOOKE uses fast syscall entry */
 #ifdef CONFIG_TRACE_IRQFLAGS
 trace_syscall_entry_irq_off:
 	/*
@@ -369,7 +368,6 @@ transfer_to_syscall:
 	andi.	r12,r9,MSR_EE
 	beq-	trace_syscall_entry_irq_off
 #endif /* CONFIG_TRACE_IRQFLAGS */
-#endif /* !CONFIG_BOOKE */
 
 /*
  * Handle a system call.
@@ -382,11 +380,6 @@ _GLOBAL(DoSyscall)
 	stw	r3,ORIG_GPR3(r1)
 	li	r12,0
 	stw	r12,RESULT(r1)
-#ifdef CONFIG_BOOKE	/* to be removed once BOOKE uses fast syscall entry */
-	lwz	r11,_CCR(r1)	/* Clear SO bit in CR */
-	rlwinm	r11,r11,0,4,2
-	stw	r11,_CCR(r1)
-#endif
 #ifdef CONFIG_TRACE_IRQFLAGS
 	/* Make sure interrupts are enabled */
 	mfmsr	r11