i386/msr: Extract and improve MSR support detection code

Currently rdmsr and wrmsr commands have own MSR support detection code.
This code is the same. So, it is duplicated. Additionally, this code
cannot be reused by others. Hence, extract this code to a function and
make it public. By the way, improve a code a bit.

Additionally, use GRUB_ERR_BAD_DEVICE instead of GRUB_ERR_BUG to signal
an error because errors encountered by this new routine are not bugs.

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: Sergii Dmytruk <sergii.dmytruk@3mdeb.com>
Reviewed-by: Ross Philipson <ross.philipson@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/commands/i386/wrmsr.c

@@ -36,26 +36,15 @@ static grub_command_t cmd_write;
 static grub_err_t
 grub_cmd_msr_write (grub_command_t cmd __attribute__ ((unused)), int argc, char **argv)
 {
-  grub_uint32_t manufacturer[3], max_cpuid, a, b, c, features, addr;
+  grub_err_t err;
+  grub_uint32_t addr;
   grub_uint64_t value;
   const char *ptr;
 
-  /*
-   * The CPUID instruction should be used to determine whether MSRs
-   * are supported. (CPUID.01H:EDX[5] = 1)
-   */
-  if (!grub_cpu_is_cpuid_supported ())
-    return grub_error (GRUB_ERR_BUG, N_("unsupported instruction"));
+  err = grub_cpu_is_msr_supported ();
 
-  grub_cpuid (0, max_cpuid, manufacturer[0], manufacturer[2], manufacturer[1]);
-
-  if (max_cpuid < 1)
-    return grub_error (GRUB_ERR_BUG, N_("unsupported instruction"));
-
-  grub_cpuid (1, a, b, c, features);
-
-  if (!(features & (1 << 5)))
-    return grub_error (GRUB_ERR_BUG, N_("unsupported instruction"));
+  if (err != GRUB_ERR_NONE)
+    return grub_error (err, N_("WRMSR is unsupported"));
 
   if (argc != 2)
     return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("two arguments expected"));