hw/arm/aspeed_ast10x0: Map the secure SRAM

hw/arm/aspeed_ast10x0: Map the secure SRAM

Some SRAM appears to be used by the Secure Boot unit and
crypto accelerators. Name it 'secure sram'.

Note, the SRAM base address was already present but unused
(the 'SBC' index is used for the MMIO peripheral).

Interestingly using CFLAGS=-Winitializer-overrides reports:

  ../hw/arm/aspeed_ast10x0.c:32:30: warning: initializer overrides prior initialization of this subobject [-Winitializer-overrides]
    [ASPEED_DEV_SBC]       = 0x7E6F2000,
                             ^~~~~~~~~~
  ../hw/arm/aspeed_ast10x0.c:24:30: note: previous initialization is here
    [ASPEED_DEV_SBC]       = 0x79000000,
                             ^~~~~~~~~~
This fixes with Zephyr:

  uart:~$ rsa test
  rsa test vector[0]:
  [00:00:26.156,000] <err> os: ***** BUS FAULT *****
  [00:00:26.157,000] <err> os:   Precise data bus error
  [00:00:26.157,000] <err> os:   BFAR Address: 0x79000000
  [00:00:26.158,000] <err> os: r0/a1:  0x79000000  r1/a2:  0x00000000  r2/a3:  0x00001800
  [00:00:26.158,000] <err> os: r3/a4:  0x79001800 r12/ip:  0x00000800 r14/lr:  0x0001098d
  [00:00:26.158,000] <err> os:  xpsr:  0x81000000
  [00:00:26.158,000] <err> os: Faulting instruction address (r15/pc): 0x0001e1bc
  [00:00:26.158,000] <err> os: >>> ZEPHYR FATAL ERROR 0: CPU exception on CPU 0
  [00:00:26.158,000] <err> os: Current thread: 0x38248 (shell_uart)
  [00:00:26.165,000] <err> os: Halting system

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Peter Delevoryas <peter@pjd.dev>
[ clg: Fixed size of Secure Boot Controller Memory ]
Signed-off-by: Cédric Le Goater <clg@kaod.org>