boot: stop making TPM PCR to measure kernel command line into configurable

Everyone appears to use PCR 8 for this, hence I think it's safe to
hardcode that in systemd too.

It's also documented, like here:

https://www.gnu.org/software/grub/manual/grub/html_node/Measured-Boot.html

or here:

https://github.com/rhboot/shim/blob/main/README.tpm

(And the previous name was a bit confusing, since we don't actually just
measure one thing anymore, but mutliple things into multiple PCRs...)

src/boot/efi/boot.c

@@ -2349,7 +2349,7 @@ static EFI_STATUS image_start(
 
 #if ENABLE_TPM
                 /* Try to log any options to the TPM, especially to catch manually edited options */
-                err = tpm_log_event(SD_TPM_PCR,
+                err = tpm_log_event(TPM_PCR_INDEX_KERNEL_PARAMETERS,
                                     (EFI_PHYSICAL_ADDRESS) (UINTN) loaded_image->LoadOptions,
                                     loaded_image->LoadOptionsSize, loaded_image->LoadOptions);
                 if (EFI_ERROR(err))

src/boot/efi/meson.build

@@ -103,7 +103,6 @@ if have_gnu_efi
         efi_conf = configuration_data()
         efi_conf.set_quoted('EFI_MACHINE_TYPE_NAME', EFI_MACHINE_TYPE_NAME)
         efi_conf.set10('ENABLE_TPM', get_option('tpm'))
-        efi_conf.set('SD_TPM_PCR', get_option('tpm-pcrindex'))
 
         foreach ctype : ['color-normal', 'color-entry', 'color-highlight', 'color-edit']
                 c = get_option('efi-' + ctype).split(',')

src/boot/efi/stub.c

@@ -148,7 +148,7 @@ EFI_STATUS efi_main(EFI_HANDLE image, EFI_SYSTEM_TABLE *sys_table) {
 
 #if ENABLE_TPM
                 /* Try to log any options to the TPM, especially manually edited options */
-                err = tpm_log_event(SD_TPM_PCR,
+                err = tpm_log_event(TPM_PCR_INDEX_KERNEL_PARAMETERS,
                                     (EFI_PHYSICAL_ADDRESS) (UINTN) loaded_image->LoadOptions,
                                     loaded_image->LoadOptionsSize, loaded_image->LoadOptions);
                 if (EFI_ERROR(err))