MIPS: fix setup of initial stack frame

To get correct stack walking and backtrace functionality in gdb,
registers fp and ra should be initialized before calling board_init_f
or board_init_r. Thus allocating stack space and zeroing it as it is
currently done in board.c becomes obsolete.
Signed-off-by: NDaniel Schwierzeck <daniel.schwierzeck@gmail.com>

arch/mips/cpu/mips32/start.S

@@ -136,10 +136,11 @@ reset:
 
 	/* Set up temporary stack */
 	li	sp, CONFIG_SYS_SDRAM_BASE + CONFIG_SYS_INIT_SP_OFFSET
+	move	fp, sp
 
 	la	t9, board_init_f
 	jr	t9
-	 nop
+	 move	ra, zero
 
 /*
  * void relocate_code (addr_sp, gd, addr_moni)
@@ -155,6 +156,7 @@ reset:
 	.ent	relocate_code
 relocate_code:
 	move	sp, a0			# set new stack pointer
+	move	fp, sp
 
 	move	s0, a1			# save gd in s0
 	move	s2, a2			# save destination address in s2
@@ -260,8 +262,9 @@ in_ram:
 	 addi	t1, 4
 
 	move	a0, s0			# a0 <-- gd
+	move	a1, s2
 	la	t9, board_init_r
 	jr	t9
-	 move	a1, s2
+	 move	ra, zero
 
 	.end	relocate_code

arch/mips/cpu/mips64/start.S

@@ -130,10 +130,11 @@ reset:
 
 	/* Set up temporary stack */
 	dli	sp, CONFIG_SYS_SDRAM_BASE + CONFIG_SYS_INIT_SP_OFFSET
+	move	fp, sp
 
 	dla	t9, board_init_f
 	jr	t9
-	 nop
+	 move	ra, zero
 
 /*
  * void relocate_code (addr_sp, gd, addr_moni)
@@ -149,6 +150,7 @@ reset:
 	.ent	relocate_code
 relocate_code:
 	move	sp, a0			# set new stack pointer
+	move	fp, sp
 
 	move	s0, a1			# save gd in s0
 	move	s2, a2			# save destination address in s2
@@ -254,8 +256,9 @@ in_ram:
 	 daddi	t1, 8
 
 	move	a0, s0			# a0 <-- gd
+	move	a1, s2
 	dla	t9, board_init_r
 	jr	t9
-	 move	a1, s2
+	 move	ra, zero
 
 	.end	relocate_code