Add support for seeed_xiao_nrf52840_kit (#6231)

* add support for seeed_xiao_nrf52840_kit

* Update platformio.ini remove board level define

variants/seeed_xiao_nrf52840_kit/platformio.ini

@@ -0,0 +1,13 @@
+; Seeed Xiao BLE: https://www.digikey.com/en/products/detail/seeed-technology-co-ltd/102010448/16652893
+[env:seeed_xiao_nrf52840_kit]
+extends = nrf52840_base
+board = xiao_ble_sense
+build_flags = ${nrf52840_base.build_flags} -Ivariants/seeed_xiao_nrf52840_kit -Isrc/platform/nrf52/softdevice -Isrc/platform/nrf52/softdevice/nrf52  -Dseeed_xiao_nrf52840_kit
+  -L "${platformio.libdeps_dir}/${this.__env__}/bsec2/src/cortex-m4/fpv4-sp-d16-hard"
+board_build.ldscript = src/platform/nrf52/nrf52840_s140_v7.ld
+build_src_filter = ${nrf52_base.build_src_filter} +<../variants/seeed_xiao_nrf52840_kit>
+lib_deps = 
+  ${nrf52840_base.lib_deps}
+debug_tool = jlink
+; If not set we will default to uploading over serial (first it forces bootloader entry by talking 1200bps to cdcacm)
+;upload_protocol = jlink