imx: bootaux: change names of MACROs used to boot MCU on iMX devices

The current bootaux supports i.MX8M and i.MX93, but the name "_M4_"
implies that the SoCs have Cortex-M4. Actually i.MX8MM/Q use Cortex-M4,
i.MX8MN/P use Cortex-M7, i.MX93 use Cortex-M33, so use "_MCU_" in place
of "_M4_" to simplify the naming.

Signed-off-by: faqiang.zhu <faqiang.zhu@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/board/kontron/sl-mx8mm/sl-mx8mm.c b/board/kontron/sl-mx8mm/sl-mx8mm.c
index ddb509e..8dcc2ea 100644
--- a/board/kontron/sl-mx8mm/sl-mx8mm.c
+++ b/board/kontron/sl-mx8mm/sl-mx8mm.c
@@ -37,7 +37,7 @@
 
 int board_phys_sdram_size(phys_size_t *size)
 {
-	u32 ddr_size = readl(M4_BOOTROM_BASE_ADDR);
+	u32 ddr_size = readl(MCU_BOOTROM_BASE_ADDR);
 
 	if (ddr_size == 4) {
 		*size = 0x100000000;
diff --git a/board/kontron/sl-mx8mm/spl.c b/board/kontron/sl-mx8mm/spl.c
index 3a919d0..b493734 100644
--- a/board/kontron/sl-mx8mm/spl.c
+++ b/board/kontron/sl-mx8mm/spl.c
@@ -106,7 +106,7 @@
 	}
 
 	gd->ram_size = size;
-	writel(size, M4_BOOTROM_BASE_ADDR);
+	writel(size, MCU_BOOTROM_BASE_ADDR);
 }
 
 int do_board_detect(void)