Documentation: arm64: Update memory.rst for TBI

Most of memory.rst was written very early, at a time where TBI (Top
Byte Ignore) was not enabled. Nowadays TBI0 is always enabled, and
TBI1 may be enabled, depending on the kernel configuration. This
means that VA bits 63:56 cannot generally be assumed to have any
particular value.

Regardless of TBI, TTBRx selection is done based on bit 55; update
memory.rst accordingly.
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20240702091349.356008-1-kevin.brodsky@arm.comSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

Documentation/arch/arm64/memory.rst

@@ -18,12 +18,10 @@ ARMv8.2 adds optional support for Large Virtual Address space. This is
 only available when running with a 64KB page size and expands the
 number of descriptors in the first level of translation.
 
-User addresses have bits 63:48 set to 0 while the kernel addresses have
-the same bits set to 1. TTBRx selection is given by bit 63 of the
-virtual address. The swapper_pg_dir contains only kernel (global)
-mappings while the user pgd contains only user (non-global) mappings.
-The swapper_pg_dir address is written to TTBR1 and never written to
-TTBR0.
+TTBRx selection is given by bit 55 of the virtual address. The
+swapper_pg_dir contains only kernel (global) mappings while the user pgd
+contains only user (non-global) mappings.  The swapper_pg_dir address is
+written to TTBR1 and never written to TTBR0.
 
 
 AArch64 Linux memory layout with 4KB pages + 4 levels (48-bit)::
@@ -72,7 +70,7 @@ Translation table lookup with 4KB pages::
             |        |         |         +-----------> [29:21] L2 index
             |        |         +---------------------> [38:30] L1 index
             |        +-------------------------------> [47:39] L0 index
-   +-------------------------------------------------> [63] TTBR0/1
+            +----------------------------------------> [55] TTBR0/1
 
 
 Translation table lookup with 64KB pages::
@@ -87,7 +85,7 @@ Translation table lookup with 64KB pages::
             |        |    +--------------------------> [41:29] L2 index
             |        +-------------------------------> [47:42] L1 index (48-bit)
             |                                          [51:42] L1 index (52-bit)
-   +-------------------------------------------------> [63] TTBR0/1
+            +----------------------------------------> [55] TTBR0/1
 
 
 When using KVM without the Virtualization Host Extensions, the