arch/riscv: Remove supervisor_trap_entry

coreboot only maintains a single trap entry, because it only runs in
machine mode.

Change-Id: I7324d9c8897d5c4e9d4784e7bc2a055890eab698
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-on: https://review.coreboot.org/22595
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/arch/riscv/trap_util.S

@@ -107,15 +107,7 @@
 
 .globl estack
   .text
-  .global  supervisor_trap_entry
-supervisor_trap_entry:
-    csrw mscratch, sp
-    # load in the top of the machine stack
-    la	sp, _estack
-    addi sp,sp,-MENTRY_FRAME_SIZE
-    save_tf
-    move  a0,sp
-    jal trap_handler
+
     .global  trap_entry
 trap_entry:
   csrw mscratch, sp