RISC-V: Add the directive for alignment of stvec's value

The stvec's value must be 4 byte alignment by specification definition.
These directives avoid to stvec be set the non-alignment value.
Signed-off-by: Zong Li <zong@andestech.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

arch/riscv/kernel/head.S

@@ -94,6 +94,7 @@ relocate:
 	or a0, a0, a1
 	sfence.vma
 	csrw sptbr, a0
+.align 2
 1:
 	/* Set trap vector to spin forever to help debug */
 	la a0, .Lsecondary_park
@@ -143,6 +144,7 @@ relocate:
 	tail smp_callin
 #endif
 
+.align 2
 .Lsecondary_park:
 	/* We lack SMP support or have too many harts, so park this hart */
 	wfi