riscv: cpu: th1520: Add a routine to bring up secondary cores

On coldboot, only HART 0 among the four HARTs of TH1520 is brought up by
hardware, and the remaining HARTs are in reset states, requiring manual
setup of reset address and deassertion to function normal. Introduce a
routine to do the work.

Signed-off-by: Yao Zi <ziyao@disroot.org>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>

arch/riscv/include/asm/arch-th1520/cpu.h

@@ -5,5 +5,6 @@
 
 #ifndef _ASM_TH1520_CPU_H_
 #define _ASM_TH1520_CPU_H_
+void th1520_kick_secondary_cores(void);
 void th1520_invalidate_pmp(void);
 #endif /* _ASM_TH1520_CPU_H_ */