soc/amd/sabrina: Disable CCP DMA and HW MODEXP

Enabling them causes firmware keyblock/preamble and/or body verification
failure. Hence disabling them to use software based verification.
Re-enable them once the issue is root-caused.

BUG=b:217414563
TEST=Build and boot to OS in Skyrim with PSP and x86 verstage.

Signed-off-by: Karthikeyan Ramasubramanian <kramasub@google.com>
Change-Id: I7e259ae5d790977d08afcb0a77f8d4f38c85f39e
Reviewed-on: https://review.coreboot.org/c/coreboot/+/66134
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/amd/sabrina/Kconfig

@@ -44,7 +44,6 @@ config SOC_SPECIFIC_OPTIONS
 	select PARALLEL_MP_AP_WORK
 	select PLATFORM_USES_FSP2_0
 	select PROVIDES_ROM_SHARING
-	select PSP_VERSTAGE_CCP_DMA if VBOOT_STARTS_BEFORE_BOOTBLOCK
 	select PSP_SUPPORTS_EFS2_RELATIVE_ADDR if VBOOT_STARTS_BEFORE_BOOTBLOCK
 	select RESET_VECTOR_IN_RAM
 	select RTC

src/soc/amd/sabrina/psp_verstage/svc.c

@@ -174,12 +174,8 @@ uint32_t svc_crypto_sha(struct sha_generic_data *sha_op, enum sha_operation_mode
 
 uint32_t svc_modexp(struct mod_exp_params *mod_exp_param)
 {
-	uint32_t retval = 0;
-	struct cmd_param_modexp param = {
-		.ptr_modexp = mod_exp_param,
-	};
-	SVC_CALL2(SVC_VERSTAGE_CMD, CMD_MODEXP, (void *)&param, retval);
-	return retval;
+	/* TODO: b/240175446 Re-enable CCP DMA and svc_modexp later. */
+	return 1;
 }
 
 uint32_t svc_ccp_dma(uint32_t spi_rom_offset, void *dest, uint32_t size)