fix(build): enforce single partition for LTO build

For example, build for PLAT=fvp SPD=spmd fails with a following error
when LTO is enabled using GCC 13.2.1:

  aarch64-none-elf/bin/ld: /tmp/ccrG0Z8D.ltrans0.ltrans.o: in function `spmd_smc_forward':
  arm-trusted-firmware/services/std_svc/spmd/spmd_main.c:749:(.text+0xbe50): undefined reference to `rdist_ctx'
  aarch64-none-elf/bin/ld: arm-trusted-firmware/services/std_svc/spmd/spmd_main.c:749:(.text+0xbe58): undefined reference to `dist_ctx'
  collect2: error: ld returned 1 exit status

Access to rdist_ctx and dist_ctx is defined using inline assembler
like
 __asm__ volatile ("ldr %0, =rdist_ctx" : "=r" (v) : "X" (rdist_ctx));

Access assembler function definitions moved to a different ltrans then
actual variables. Partitioner doesn't take into account defined and
used symbols in inline assembler. Depending on compiler partitioner
decision the same code builds for some platforms successfully.

This is a known gcc problem
1. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57703
2. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46820

TF-A source code isn't that big and enforcing single partitioning will
not affect build performance, but will fix problems with 'undefined
references' related to inline assembler.

Change-Id: I72955ab0318f72b588d3a246824f99a48a92d8ef
Signed-off-by: Andrey Skvortsov <andrej.skvortzov@gmail.com>

Makefile

@@ -325,6 +325,7 @@ else ifeq ($($(ARCH)-ld-id),gnu-gcc)
 	ifeq ($(ENABLE_LTO),1)
 		ifeq (${ARCH},aarch64)
 			TF_LDFLAGS	+=	-flto -fuse-linker-plugin
+			TF_LDFLAGS      +=	-flto-partition=one
 		endif
 	endif #(ENABLE_LTO)