riscv: allow to enable SHOW_REGS in main U-Boot only

To minimize SPL size it is reasonable to disable SHOW_REGS. For main U-Boot
the size restrictions are much more relaxed.

* Provide separate Kconfig symbols for SPL and main U-Boot.
* Add a help text.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 4e228a6..fd1f5f8 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -439,6 +439,18 @@
 
 config SHOW_REGS
 	bool "Show registers on unhandled exception"
+	help
+	  By default only the program counter and the return address register
+	  are shown in crash dumps. Enable this symbol to show all registers in
+	  main U-Boot.
+
+config SPL_SHOW_REGS
+	bool "In SPL show registers on unhandled exception"
+	depends on SPL
+	help
+	  By default only the program counter and the return address register
+	  are shown in crash dumps. Enable this symbol to show all registers in
+	  SPL.
 
 config RISCV_PRIV_1_9
 	bool "Use version 1.9 of the RISC-V priviledged specification"