armv7: do not relocate _start twice

The _start symbol is already relocated, so do not add the relocation the second
time in c_runtime_cpu_setup.

This fixes e.g. the abort exception handling path, which ended in double fault
due to bad address in VBAR.

Signed-off-by: Vincent Stehlé <v-stehle@ti.com>
Reported-by: Lubomir Popov <lpopov@mm-sol.com>

arch/arm/cpu/armv7/start.S

@@ -254,7 +254,6 @@ ENTRY(c_runtime_cpu_setup)
 #if !defined(CONFIG_TEGRA)
 	/* Set vector address in CP15 VBAR register */
 	ldr     r0, =_start
-	add     r0, r0, r9
 	mcr     p15, 0, r0, c12, c0, 0  @Set VBAR
 #endif /* !Tegra */