[lib][uefi] Allow complete platform customization for UEFI

Added platform_setup_system_table, where platform/vendor can
make arbitrary changes to UEFI's system table, overriding
any of the UEFI protocols with custom one.

lib/uefi/uefi.cpp

@@ -41,6 +41,7 @@
 #include "runtime_service_provider.h"
 #include "switch_stack.h"
 #include "text_protocol.h"
+#include "uefi_platform.h"
 
 namespace {
 
@@ -122,6 +123,7 @@ int load_sections_and_execute(bdev_t *dev,
       reinterpret_cast<EfiConfigurationTable *>(alloc_page(PAGE_SIZE));
   memset(table.configuration_table, 0, PAGE_SIZE);
   setup_configuration_table(&table);
+  platform_setup_system_table(&table);
 
   constexpr size_t kStackSize = 8 * 1024ul * 1024;
   auto stack = reinterpret_cast<char *>(alloc_page(kStackSize, 23));

lib/uefi/uefi_platform.cpp

@@ -99,3 +99,8 @@ __WEAK EfiStatus exit_boot_services(EfiHandle image_handle, size_t map_key) {
   printf("%s is called\n", __FUNCTION__);
   return SUCCESS;
 }
+
+__WEAK EfiStatus platform_setup_system_table(EfiSystemTable *table) {
+  printf("%s is called\n", __FUNCTION__);
+  return SUCCESS;
+}

lib/uefi/uefi_platform.h

@@ -41,4 +41,7 @@ EfiStatus select_device_trees(struct GblEfiOsConfigurationProtocol *self,
                               GblEfiVerifiedDeviceTree *device_trees,
                               size_t num_device_trees);
 EfiStatus exit_boot_services(EfiHandle image_handle, size_t map_key);
+
+EfiStatus platform_setup_system_table(EfiSystemTable *table);
+
 #endif