redhat/configs: set CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB default value

JIRA: https://issues.redhat.com/browse/RHEL-114162

Upstream status: RHEL-only

IMA_KEXEC_EXTRA_MEMORY_KB depends on IMA_KEXEC, and IMA_KEXEC depends
on HAVE_IMA_KEXEC. So here set the default value for
CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB to fix the building warning:

    Found unset config items in x86_64 rhel, please set them to an appropriate value
    CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB=0

Signed-off-by: Baoquan He <bhe@redhat.com>

Author: Baoquan He

redhat/configs/common/generic/CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB

@@ -0,0 +1 @@
+CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB=0