kboot: Add option to parse 32-bit quantity

The type that's exposed from sysfs' memory map is 32-bit and so is the
data-type of memory description.

Sponsored by:		Netflix
Reviewed by:		kevans, andrew,	jhibbits
Differential Revision:	https://reviews.freebsd.org/D49856

stand/kboot/include/util.h

@@ -7,4 +7,5 @@
 #pragma once
 
 bool file2str(const char *fn, char *buffer, size_t buflen);
+bool file2u32(const char *fn, uint32_t *val);
 bool file2u64(const char *fn, uint64_t *val);

stand/kboot/libkboot/util.c

@@ -44,3 +44,16 @@ file2u64(const char *fn, uint64_t *val)
 	*val = v;
 	return true;
 }
+
+bool
+file2u32(const char *fn, uint32_t *val)
+{
+	unsigned long v;
+	char buffer[80];
+
+	if (!file2str(fn, buffer, sizeof(buffer)))
+		return false;
+	v = strtoul(buffer, NULL, 0);	/* XXX check return values? */
+	*val = v;
+	return true;
+}