Add _extram_start & _extram_end for Teensy 4.1

teensy4/imxrt1062_t41.ld

@@ -68,6 +68,7 @@ SECTIONS
 
 	.bss.extram (NOLOAD) : {
 		*(.externalram)
+		. = ALIGN(32);
 	} > ERAM
 
 	.text.csf : {
@@ -90,6 +91,9 @@ SECTIONS
 	_heap_start = ADDR(.bss.dma) + SIZEOF(.bss.dma);
 	_heap_end = ORIGIN(RAM) + LENGTH(RAM);
 
+	_extram_start = ADDR(.bss.extram);
+	_extram_end = ADDR(.bss.extram) + SIZEOF(.bss.extram);
+
 	_itcm_block_count = (SIZEOF(.text.itcm) + SIZEOF(.ARM.exidx) + 0x7FFF) >> 15;
 	_flexram_bank_config = 0xAAAAAAAA | ((1 << (_itcm_block_count * 2)) - 1);
 	_estack = ORIGIN(DTCM) + ((16 - _itcm_block_count) << 15);