dracut-functions: add a helper to check if kernel module is available

It's like check_kernel_config, help to check if a kernel module is
enabled (cover built-in or compiled module case).

Signed-off-by: Kairui Song <kasong@redhat.com>

dracut-functions.sh

@@ -674,6 +674,11 @@ check_kernel_config()
     return 1
 }
 
+# 0 if the kernel module is either built-in or available
+# 1 if the kernel module is not enabled
+check_kernel_module() {
+    modprobe -S $kernel --dry-run $1 &>/dev/null || return 1
+}
 
 # get_cpu_vendor
 # Only two values are returned: AMD or Intel