Add RW memory layout TE layout

XFERLIST_RW_MEM_LAYOUT is used to specify an extent of read-write memory
that a client can use.

source/transfer_list.rst

@@ -511,6 +511,7 @@ The following entry types are currently defined:
 - ACPI table aggregate entry: tag_id = 4 (:numref:`acpi_aggr_entry`).
 - TPM event log entry: tag_id = 5 (:numref:`tpm_evlog_entry`).
 - TPM CRB base entry: tag_id = 6 (:numref:`tpm_crb_base_entry`).
+- Read-Write Memory Layout: tag_id = 7 (:numref:`rw_mem_layout`).
 - Entries related to Trusted Firmware (:numref:`tf_entries`).
 
 .. _void_entry:
@@ -820,6 +821,48 @@ and reserved for use as a TPM Command Response Buffer interface.
      - Size of CRB.
 
 
+.. _rw_mem_layout:
+
+Read-Write Memory Layout Entry Layout (XFERLIST_RW_MEM_LAYOUT)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This type defines the layout of a region of read-write memory that a client can
+allocate into its memory map. If other memory types are required (i.e.
+read-only memory), separate TE's should be defined.
+
+.. _tab_sram_mem_conf:
+.. list-table:: Layout for a RW memory layout entry
+   :widths: 2 5 5 6
+
+   * - Field
+     - Size (bytes)
+     - Offset (bytes)
+     - Description
+
+   * - tag_id
+     - 0x3
+     - 0x0
+     - The tag_id field must be set to **7**.
+
+   * - hdr_size
+     - 0x1
+     - 0x3
+     - |hdr_size_desc|
+
+   * - data_size
+     - 0x4
+     - 0x4
+     - The size of the layout in bytes.
+
+   * - addr
+     - `sizeof(uintptr_t)`
+     - hdr_size
+     - The base address of the memory region.
+
+   * - size
+     - `sizeof(size_t)`
+     - `hdr_size + sizeof(uintrptr_t)`
+     - The size of the memory region.
 
 .. _tf_entries: