Rename BLUEPILL_F103XX to PILL_F103XX

Comment from @BennehBoy about 'PILL' style boards handled in the core:

> There's a fair bit of fragmentation in the variants folder currently,
> the BLUEPILL_F103XX folder handles generic blue & black pills

Co-authored-by: BennehBoy <bennyboy@benneh.net>
Signed-off-by: Frederic.Pillon <frederic.pillon@st.com>

Author: fpistm

boards.txt

@@ -612,37 +612,37 @@ GenF1.menu.pnum.BLUEPILL_F103C6.upload.maximum_size=32768
 GenF1.menu.pnum.BLUEPILL_F103C6.upload.maximum_data_size=10240
 GenF1.menu.pnum.BLUEPILL_F103C6.build.board=BLUEPILL_F103C6
 GenF1.menu.pnum.BLUEPILL_F103C6.build.product_line=STM32F103x6
-GenF1.menu.pnum.BLUEPILL_F103C6.build.variant=BLUEPILL_F103XX
+GenF1.menu.pnum.BLUEPILL_F103C6.build.variant=PILL_F103XX
 
 # BLUEPILL_F103C8 board
 GenF1.menu.pnum.BLUEPILL_F103C8=BluePill F103C8
 GenF1.menu.pnum.BLUEPILL_F103C8.upload.maximum_size=65536
 GenF1.menu.pnum.BLUEPILL_F103C8.upload.maximum_data_size=20480
 GenF1.menu.pnum.BLUEPILL_F103C8.build.board=BLUEPILL_F103C8
 GenF1.menu.pnum.BLUEPILL_F103C8.build.product_line=STM32F103xB
-GenF1.menu.pnum.BLUEPILL_F103C8.build.variant=BLUEPILL_F103XX
+GenF1.menu.pnum.BLUEPILL_F103C8.build.variant=PILL_F103XX
 
 GenF1.menu.pnum.BLUEPILL_F103C8B=BluePill F103C8 (128k)
 GenF1.menu.pnum.BLUEPILL_F103C8B.upload.maximum_size=131072
 GenF1.menu.pnum.BLUEPILL_F103C8B.upload.maximum_data_size=20480
 GenF1.menu.pnum.BLUEPILL_F103C8B.build.board=BLUEPILL_F103C8
 GenF1.menu.pnum.BLUEPILL_F103C8B.build.product_line=STM32F103xB
-GenF1.menu.pnum.BLUEPILL_F103C8B.build.variant=BLUEPILL_F103XX
+GenF1.menu.pnum.BLUEPILL_F103C8B.build.variant=PILL_F103XX
 
 # BLACKPILL_F103C8 board
 GenF1.menu.pnum.BLACKPILL_F103C8=BlackPill F103C8
 GenF1.menu.pnum.BLACKPILL_F103C8.upload.maximum_size=65536
 GenF1.menu.pnum.BLACKPILL_F103C8.upload.maximum_data_size=20480
 GenF1.menu.pnum.BLACKPILL_F103C8.build.board=BLACKPILL_F103C8
 GenF1.menu.pnum.BLACKPILL_F103C8.build.product_line=STM32F103xB
-GenF1.menu.pnum.BLACKPILL_F103C8.build.variant=BLUEPILL_F103XX
+GenF1.menu.pnum.BLACKPILL_F103C8.build.variant=PILL_F103XX
 
 GenF1.menu.pnum.BLACKPILL_F103C8B=BlackPill F103C8 (128k)
 GenF1.menu.pnum.BLACKPILL_F103C8B.upload.maximum_size=131072
 GenF1.menu.pnum.BLACKPILL_F103C8B.upload.maximum_data_size=20480
 GenF1.menu.pnum.BLACKPILL_F103C8B.build.board=BLACKPILL_F103C8
 GenF1.menu.pnum.BLACKPILL_F103C8B.build.product_line=STM32F103xB
-GenF1.menu.pnum.BLACKPILL_F103C8B.build.variant=BLUEPILL_F103XX
+GenF1.menu.pnum.BLACKPILL_F103C8B.build.variant=PILL_F103XX
 
 # MAPLEMINI_F103CB board
 GenF1.menu.pnum.MAPLEMINI_F103CB=Maple Mini F103CB