BIOS: support readonly attributes

Since the P10 system has BMC to manager the BIOS attributes,
and the BMC side does not know the attribute values of the BIOS,
it should allow the OOB interface(Host) to be able to set BIOS
readOnly attributes, while still preventing the redfish-doPATCH
operation on it.

Tested: if the readOnly attribute of the pvm_system_name is true,
so we can use `pldmtool` to update the BIOS attributes.

pldmtool bios SetBIOSAttributeCurrentValue -a pvm_system_name -d XXX
{
    "Response": "SUCCESS"
}

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: Iabcb5c2400eb0a5c208cc76180d4b07e02457f44
diff --git a/libpldmresponder/bios_string_attribute.cpp b/libpldmresponder/bios_string_attribute.cpp
index 6aa3dc5..d89ab49 100644
--- a/libpldmresponder/bios_string_attribute.cpp
+++ b/libpldmresponder/bios_string_attribute.cpp
@@ -62,7 +62,7 @@
     const pldm_bios_attr_val_table_entry* attrValueEntry,
     const pldm_bios_attr_table_entry*, const BIOSStringTable&)
 {
-    if (readOnly || !dBusMap.has_value())
+    if (!dBusMap.has_value())
     {
         return;
     }
@@ -74,7 +74,7 @@
 
 std::string BIOSStringAttribute::getAttrValue()
 {
-    if (readOnly || !dBusMap.has_value())
+    if (!dBusMap.has_value())
     {
         return stringInfo.defString;
     }