vc/google: Show different logos for different ChromeOS devices

This commit adds support for showing different logos on the ChromeOS
firmware splash screen based on the device model (between
Chromebook-Plus and regular ChromeOS devices like Chromebook and
Chromebox). This allows OEMs to customize the branding on their
devices.

This patch also introduces three new Kconfigs:
 - CHROMEOS_FW_SPLASH_SCREEN
 - CHROMEOS_LOGO_PATH
 - CHROMEBOOK_PLUS_LOGO_PATH
which allow users to enable the fw splash screen feature in the
vendorcode. Previously, we were using the BMP_LOGO Kconfig in
drivers/intel/fsp2_0, but we didn't want the top level Kconfigs to be
located inside the architecture specific files.

BUG=b:317880956
BRANCH=None
TEST=emerge-rex coreboot chromeos-bootimage
     verify that FW splash screen appears

Change-Id: I56613d1e7e81e25b31ad034edae0f716c94c4960
Signed-off-by: Shelley Chen <shchen@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/79775
Reviewed-by: Kapil Porwal <kapilporwal@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>

src/include/bootsplash.h

@@ -15,7 +15,11 @@ void set_bootsplash(unsigned char *framebuffer, unsigned int x_resolution,
 		    unsigned int y_resolution, unsigned int bytes_per_line,
 		    unsigned int fb_resolution);
 
-
+/*
+ * Allow platform-specific BMP logo overrides via HAVE_CUSTOM_BMP_LOGO config.
+ * For example: Introduce configurable BMP logo for customization on platforms like ChromeOS
+ */
+const char *bmp_logo_filename(void);
 void bmp_load_logo(uint32_t *logo_ptr, uint32_t *logo_size);
 void bmp_release_logo(void);