redhat/configs: Disable CONFIG_EFI_MIXED in RHEL

JIRA: https://issues.redhat.com/browse/RHEL-115521

Upstream Status: git@gitlab.com:cki-project/kernel-ark.git

Conflicts:
   centos-stream-10 does not include any redhat/configs/fedora/
   configs. Thus, a rename from redhat/configs/common/ to
   redhat/configs/fedora/ in kernel-ark becomes a remove from
   redhat/configs/common/ in centos-stream-10.

commit bbfe516bba796cbca8702877f77350482fccc72c
Author: Lenny Szubowicz <lszubowi@redhat.com>
Date:   Mon Sep 22 20:50:57 2025 -0400

    redhat/configs: Disable CONFIG_EFI_MIXED in RHEL

    Disable CONFIG_EFI_MIXED in RHEL but keep it enabled in Fedora.

    CONFIG_EFI_MIXED is an X86_64-only parameter that enables support
    in the kernel for booting and running a 64-bit kernel on an X86 system
    that has 32-bit EFI firmware even though the processor is 64-bit capable.

    Such systems have never been supported by RHEL. CONFIG_EFI_MIXED adds some
    code and complexity to the EFI stub. It also adds some marginal overhead
    to EFI runtime calls. Therefore, remove it from RHEL.

    Signed-off-by: Lenny Szubowicz <lszubowi@redhat.com>

Signed-off-by: Lenny Szubowicz <lszubowi@redhat.com>

Author: LennySzubowicz

redhat/configs/common/generic/x86/CONFIG_EFI_MIXED

@@ -0,0 +1 @@
+# CONFIG_EFI_MIXED is not set