x86/boot: Load microcode much earlier on boot

Following commit cd7cc5320b ("x86/boot: add start and size fields to struct
boot_module"), bootstrap_map*() works as soon as boot_info is populated.

Resolve the TODO, and move microcode loading to be the eariest action after
establishing a console.

A sample boot now looks like:

  (XEN) Xen version 4.20-unstable (andrew@eng.citrite.net) (gcc (Debian 12.2.0-14) 12.2.0) debug=y Tue Nov 19 21:44:46 GMT 2024
  (XEN) Latest ChangeSet: Wed Dec 6 21:54:55 2023 git:1ab612848a23
  (XEN) build-id: 52fe616d1b3a2a2cb44775815507d02cca73315d
  (XEN) CPU Vendor: AMD, Family 25 (0x19), Model 1 (0x1), Stepping 1 (raw 00a00f11)
  (XEN) BSP microcode revision: 0x0a001137
  (XEN) microcode: CPU0 updated from revision 0xa001137 to 0xa0011d5, date = 2024-02-23
  (XEN) Bootloader: GRUB 2.06

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/setup.c

@@ -1160,6 +1160,13 @@ void asmlinkage __init noreturn __start_xen(void)
     xhci_dbc_uart_init();
     console_init_preirq();
 
+    /*
+     * Try to load microcode as early as possible, although wait until after
+     * configuring the console(s).
+     */
+    early_cpu_init(true);
+    early_microcode_init(bi);
+
     if ( pvh_boot )
         pvh_print_info();
 
@@ -1312,9 +1319,6 @@ void asmlinkage __init noreturn __start_xen(void)
     else
         panic("Bootloader provided no memory information\n");
 
-    /* This must come before e820 code because it sets paddr_bits. */
-    early_cpu_init(true);
-
     /* Choose shadow stack early, to set infrastructure up appropriately. */
     if ( !boot_cpu_has(X86_FEATURE_CET_SS) )
         opt_xen_shstk = 0;
@@ -1416,12 +1420,6 @@ void asmlinkage __init noreturn __start_xen(void)
         if ( bi->mods[i].start & (PAGE_SIZE - 1) )
             panic("Bootloader didn't honor module alignment request\n");
 
-    /*
-     * TODO: load ucode earlier once multiboot modules become accessible
-     * at an earlier stage.
-     */
-    early_microcode_init(bi);
-
     if ( xen_phys_start )
     {
         struct boot_module *xen = &bi->mods[bi->nr_modules];