armv8: mach-k3: correct define checking for AM625/AM642 memory maps

Using CONFIG_IS_ENABLED breaks accessing memory map structure when
doing a A53 SPL build for AM625 and AM642 platforms. This is due to
'abc if CONFIG_SPL_BUILD is defined and CONFIG_SPL_FOO is set to 'y''
in which there is no CONFIG_SPL_SOC_K3_AM625/CONFIG_SPL_SOC_K3_AM642
defined in the configuration.

For the A53 SPL builds on these platform to access the memory mapping
which it will need for enabling the mmu/cache it must use #if defined(X)
checks and not CONFIG_IS_ENABLED.

Cc: Suman Anna <s-anna@ti.com>
Cc: Neha Francis <n-francis@ti.com>
Signed-off-by: Matt Ranostay <mranostay@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

arch/arm/mach-k3/arm64-mmu.c

@@ -222,7 +222,7 @@ struct mm_region *mem_map = j721s2_mem_map;
 
 #endif /* CONFIG_SOC_K3_J721S2 */
 
-#if (CONFIG_IS_ENABLED(SOC_K3_AM642) || CONFIG_IS_ENABLED(SOC_K3_AM625))
+#if defined(CONFIG_SOC_K3_AM642) || defined(CONFIG_SOC_K3_AM625)
 /* NR_DRAM_BANKS + 32bit IO + 64bit IO + terminator */
 #define NR_MMU_REGIONS	(CONFIG_NR_DRAM_BANKS + 3)