Fix Grand Central SD dependency (#21660)

Co-authored-by: Scott Lahteine <github@thinkyhead.com>

ini/samd51.ini

@@ -20,8 +20,7 @@ build_unflags  = -std=gnu++11
 src_filter     = ${common.default_src_filter} +<src/HAL/SAMD51>
 lib_deps       = ${common.lib_deps}
   SoftwareSerialM
-  Adafruit SPIFlash
 extra_scripts  = ${common.extra_scripts}
   pre:buildroot/share/PlatformIO/scripts/SAMD51_grandcentral_m4.py
-custom_marlin.SDSUPPORT = SdFat - Adafruit Fork
+custom_marlin.SDSUPPORT = SdFat - Adafruit Fork, Adafruit SPIFlash
 debug_tool     = jlink