riscv: catch up with EARLY_PRINTF changes

On this platform early console access is possible via SBI. Follow recent
changes to EARLY_PRINTF option and give it a named constant.

Update the commented option in GENERIC so that it compiles.

Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D44100

sys/riscv/conf/GENERIC

@@ -165,7 +165,7 @@ options 	WITNESS			# Enable checks to detect deadlocks and cycles
 options 	WITNESS_SKIPSPIN	# Don't run witness on spinlocks for speed
 options 	MALLOC_DEBUG_MAXZONES=8	# Separate malloc(9) zones
 options 	ALT_BREAK_TO_DEBUGGER	# Enter debugger on keyboard escape sequence
-# options 	EARLY_PRINTF
+# options 	EARLY_PRINTF=sbi
 options 	VERBOSE_SYSINIT=0	# Support debug.verbose_sysinit, off by default
 
 # Kernel dump features.

sys/riscv/riscv/riscv_console.c

@@ -110,7 +110,7 @@ riscv_putc(int c)
 	sbi_console_putchar(c);
 }
 
-#ifdef EARLY_PRINTF
+#if CHECK_EARLY_PRINTF(sbi)
 early_putc_t *early_putc = riscv_putc;
 #endif
 

sys/sys/systm.h

@@ -215,6 +215,7 @@ extern early_putc_t *early_putc;
 #define	early_printf_ns8250	3
 #define	early_printf_pl011	4
 #define	early_printf_snps	5
+#define	early_printf_sbi	6
 #else
 #define	CHECK_EARLY_PRINTF(x)	0
 #endif