Kconfig: j721s2: Change K3_MCU_SCRATCHPAD_BASE to non firewalled region

On K3 HS-SE devices all the firewalls are locked by default
until sysfw comes up. Rom configures some of the firewall for its usage
along with the SRAM for R5 but the PSRAM region is still locked.

The K3 MCU Scratchpad for j721s2 was set to a PSRAM region triggering the
firewall exception before sysfw came up. The exception started happening
after adding multi dtb support that accesses the scratchpad for reading
EEPROM contents.

Old map:
┌─────────────────────────────────────┐ 0x41c00000
│                 SPL                 │
├─────────────────────────────────────┤ 0x41c61f20 (approx)
│                STACK                │
├─────────────────────────────────────┤ 0x41c65f20
│             Global data             │
│  sizeof(struct global_data) = 0xd8  │
├─────────────────────────────────────┤ gd->malloc_base = 0x41c66000
│                HEAP                 │
│  CONFIG_SYS_MALLOC_F_LEN = 0x10000  │
├─────────────────────────────────────┤ CONFIG_SPL_BSS_START_ADDR
│               SPL BSS               │ (0x41c76000)
│  CONFIG_SPL_BSS_MAX_SIZE = 0xA000   │
├─────────────────────────────────────┤ (0x41c80000)
│               DM DATA               │
├─────────────────────────────────────┤ (0x41c84130) (approx)
│                EMPTY                │
└─────────────────────────────────────┘ CONFIG_SYS_K3_BOOT_PARAM_TABLE_INDEX
				        (0x41cffbfc)

New map:
┌─────────────────────────────────────┐ 0x41c00000
│                 SPL                 │
├─────────────────────────────────────┤ 0x41c61f20 (approx)
│                STACK                │
├─────────────────────────────────────┤ 0x41c65f20
│             Global data             │
│  sizeof(struct global_data) = 0xd8  │
├─────────────────────────────────────┤ gd->malloc_base = 0x41c66000
│                HEAP                 │
│  CONFIG_SYS_MALLOC_F_LEN = 0x10000  │
├─────────────────────────────────────┤ CONFIG_SPL_BSS_START_ADDR
│               SPL BSS               │ (0x41c76000)
│  CONFIG_SPL_BSS_MAX_SIZE = 0xA000   │
├─────────────────────────────────────┤ (0x41c80000)
│               DM DATA               │
├─────────────────────────────────────┤ (0x41c84130) (approx)
│                EMPTY                │
├─────────────────────────────────────┤ SYS_K3_MCU_SCRATCHPAD_BASE
│              SCRATCHPAD             │ (0x41cff9fc)
│ SYS_K3_MCU_SCRATCHPAD_SIZE = 0x200  │
└─────────────────────────────────────┘ CONFIG_SYS_K3_BOOT_PARAM_TABLE_INDEX
				        (0x41cffbfc)

Reviewed-by: Kamlesh Gurudasani <kamlesh@ti.com>
Signed-off-by: Manorit Chawdhry <m-chawdhry@ti.com>