enable the Bus Pirate adapter by default on most systems

Also convert the Bus Pirate to the common PROCESS_ADAPTERS logic.

Change-Id: Ifa8ebcee380c16d7e308ba7a75dbffdb74208285
Signed-off-by: R. Diez <rdiezmail-openocd@yahoo.de>
Reviewed-on: https://review.openocd.org/c/openocd/+/8533
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: R. Diez <rdiez-2006@rd10.de>
Tested-by: jenkins

src/jtag/drivers/Makefile.am

@@ -143,7 +143,7 @@ endif
 if ARMJTAGEW
 DRIVERFILES += %D%/arm-jtag-ew.c
 endif
-if BUSPIRATE
+if BUS_PIRATE
 DRIVERFILES += %D%/buspirate.c
 endif
 if REMOTE_BITBANG

src/jtag/interfaces.c

@@ -102,7 +102,7 @@ struct adapter_driver *adapter_drivers[] = {
 #if BUILD_ARMJTAGEW == 1
 		&armjtagew_adapter_driver,
 #endif
-#if BUILD_BUSPIRATE == 1
+#if BUILD_BUS_PIRATE == 1
 		&buspirate_adapter_driver,
 #endif
 #if BUILD_REMOTE_BITBANG == 1