pc: Factor common code out of pc_boot_set() and cmos_init()

Code duplicated in commit 0ecdffbb.  The two versions are similar, but
not identical:

* cmos_init() reports errors to stderr, pc_boot_set() via
  qemu_error().  The latter is fine for both, so pick that for the
  common code.

* cmos_init() obeys fd_bootchk, pc_boot_set() ignores it.  Make it a
  parameter of the common code.

hw/pc.c

@@ -230,12 +230,9 @@ static int boot_device2nibble(char boot_device)
     return 0;
 }
 
-/* copy/pasted from cmos_init, should be made a general function
- and used there as well */
-static int pc_boot_set(void *opaque, const char *boot_device)
+static int set_boot_dev(RTCState *s, const char *boot_device, int fd_bootchk)
 {
 #define PC_MAX_BOOT_DEVICES 3
-    RTCState *s = (RTCState *)opaque;
     int nbds, bds[3] = { 0, };
     int i;
 
@@ -253,16 +250,20 @@ static int pc_boot_set(void *opaque, const char *boot_device)
         }
     }
     rtc_set_memory(s, 0x3d, (bds[1] << 4) | bds[0]);
-    rtc_set_memory(s, 0x38, (bds[2] << 4));
+    rtc_set_memory(s, 0x38, (bds[2] << 4) | (fd_bootchk ? 0x0 : 0x1));
     return(0);
 }
 
+static int pc_boot_set(void *opaque, const char *boot_device)
+{
+    return set_boot_dev(opaque, boot_device, 0);
+}
+
 /* hd_table must contain 4 block drivers */
 static void cmos_init(ram_addr_t ram_size, ram_addr_t above_4g_mem_size,
                       const char *boot_device, DriveInfo **hd_table)
 {
     RTCState *s = rtc_state;
-    int nbds, bds[3] = { 0, };
     int val;
     int fd0, fd1, nb;
     int i;
@@ -301,22 +302,9 @@ static void cmos_init(ram_addr_t ram_size, ram_addr_t above_4g_mem_size,
     rtc_set_memory(s, 0x5f, smp_cpus - 1);
 
     /* set boot devices, and disable floppy signature check if requested */
-#define PC_MAX_BOOT_DEVICES 3
-    nbds = strlen(boot_device);
-    if (nbds > PC_MAX_BOOT_DEVICES) {
-        fprintf(stderr, "Too many boot devices for PC\n");
+    if (set_boot_dev(s, boot_device, fd_bootchk)) {
         exit(1);
     }
-    for (i = 0; i < nbds; i++) {
-        bds[i] = boot_device2nibble(boot_device[i]);
-        if (bds[i] == 0) {
-            fprintf(stderr, "Invalid boot device for PC: '%c'\n",
-                    boot_device[i]);
-            exit(1);
-        }
-    }
-    rtc_set_memory(s, 0x3d, (bds[1] << 4) | bds[0]);
-    rtc_set_memory(s, 0x38, (bds[2] << 4) | (fd_bootchk ?  0x0 : 0x1));
 
     /* floppy type */