efi/gop: Use helper macros for populating lfb_base

Use the lower/upper_32_bits macros from kernel.h to initialize
si->lfb_base and si->ext_lfb_base.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200320020028.1936003-8-nivedita@alum.mit.eduSigned-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/libstub/gop.c

@@ -158,8 +158,8 @@ static efi_status_t setup_gop(struct screen_info *si, efi_guid_t *proto,
 	si->lfb_height = info->vertical_resolution;
 
 	fb_base		 = efi_table_attr(mode, frame_buffer_base);
-	si->lfb_base	 = fb_base;
-	si->ext_lfb_base = (u64)(unsigned long)fb_base >> 32;
+	si->lfb_base	 = lower_32_bits(fb_base);
+	si->ext_lfb_base = upper_32_bits(fb_base);
 	if (si->ext_lfb_base)
 		si->capabilities |= VIDEO_CAPABILITY_64BIT_BASE;