ARC: entry: Add more common chores to EXCEPTION_PROLOGUE

THe high level structure of most ARC exception handlers is
 1. save regfile with EXCEPTION_PROLOGUE
 2. setup r0: EFA (not part of pt_regs)
 3. setup r1: pointer to pt_regs (SP)
 4. drop down to pure kernel mode (from exception)
 5. call the Linux "C" handler

Remove the boiler plate code by moving #2, #3, #4 into #1.

The exceptions to most exceptions are syscall Trap and Machine check
which don't do some of above for various reasons, so call a newly
introduced variant EXCEPTION_PROLOGUE_KEEP_AE (same as original
EXCEPTION_PROLOGUE)

Tested-by: Pavel Kozlov <Pavel.Kozlov@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@kernel.org>

arch/arc/include/asm/entry-compact.h

@@ -140,7 +140,7 @@
  *
  * After this it is safe to call the "C" handlers
  *-------------------------------------------------------------*/
-.macro EXCEPTION_PROLOGUE
+.macro EXCEPTION_PROLOGUE_KEEP_AE
 
 	/* Need at least 1 reg to code the early exception prologue */
 	PROLOG_FREEUP_REG r9, @ex_saved_reg1
@@ -179,6 +179,16 @@
 	; OUTPUT: r10 has ECR expected by EV_Trap
 .endm
 
+.macro EXCEPTION_PROLOGUE
+
+	EXCEPTION_PROLOGUE_KEEP_AE	; return ECR in r10
+
+	lr  r0, [efa]
+	mov r1, sp
+
+	FAKE_RET_FROM_EXCPN		; clobbers r9
+.endm
+
 /*--------------------------------------------------------------
  * Restore all registers used by system call or Exceptions
  * SP should always be pointing to the next free stack element