armv7m: Disable D-cache when booting nommu(ARMv7M) Linux kernel

Disable D-Cache is required when booting nommu Linux kernel.
(please see Linux kernel source "arch/arm/kernel/head-nommu.S")

U-Boot is enabled D-cache and I-Cache at startup.
However, it does not disable D-Cache before
booting nommu Linux kernel.
Therefore, I call dcache_disable()
when the CPU is ARMv7M to fix this problem.

Signed-off-by: Toshifumi NISHINAGA <tnishinaga.dev@gmail.com>

arch/arm/lib/bootm.c

@@ -360,6 +360,7 @@ static void boot_jump_linux(bootm_headers_t *images, int flag)
 #ifdef CONFIG_CPU_V7M
 	ulong addr = (ulong)kernel_entry | 1;
 	kernel_entry = (void *)addr;
+	dcache_disable();
 #endif
 	s = getenv("machid");
 	if (s) {