Move pthread-specific data into TLS

1. Move pthread-specific data files from sched/pthread/ to libs/libc/pthread.
2. Remove pthread-specific data functions from syscalls.
3. Implement tls_alloc() and tls_free() with system calls.
4. Reimplement pthread_key_create() and pthread_key_free() using tls_alloc() and tls_free().
5. Reimplement pthread_set_specific() and pthread_get_specicif() using tls_set_value() and tls_get_value()

boards/arm/stm32f0l0g0/b-l072z-lrwan1/configs/adc/defconfig

@@ -32,7 +32,7 @@ CONFIG_MAX_TASKS=8
 CONFIG_MAX_WDOGPARMS=2
 CONFIG_NFILE_DESCRIPTORS=6
 CONFIG_NFILE_STREAMS=6
-CONFIG_NPTHREAD_KEYS=0
+CONFIG_TLS_NELEM=0
 CONFIG_NSH_ARCHINIT=y
 CONFIG_NSH_BUILTIN_APPS=y
 CONFIG_NSH_FILEIOSIZE=64

boards/arm/stm32f0l0g0/b-l072z-lrwan1/configs/nsh/defconfig

@@ -29,7 +29,7 @@ CONFIG_MAX_TASKS=8
 CONFIG_MAX_WDOGPARMS=2
 CONFIG_NFILE_DESCRIPTORS=6
 CONFIG_NFILE_STREAMS=6
-CONFIG_NPTHREAD_KEYS=0
+CONFIG_TLS_NELEM=0
 CONFIG_NSH_BUILTIN_APPS=y
 CONFIG_NSH_FILEIOSIZE=64
 CONFIG_NSH_LINELEN=64

boards/arm/stm32f0l0g0/b-l072z-lrwan1/configs/nxlines_oled/defconfig

@@ -35,7 +35,7 @@ CONFIG_MAX_WDOGPARMS=2
 CONFIG_MQ_MAXMSGSIZE=64
 CONFIG_NFILE_DESCRIPTORS=6
 CONFIG_NFILE_STREAMS=6
-CONFIG_NPTHREAD_KEYS=0
+CONFIG_TLS_NELEM=0
 CONFIG_NSH_ARCHINIT=y
 CONFIG_NSH_BUILTIN_APPS=y
 CONFIG_NSH_FILEIOSIZE=64

boards/arm/stm32f0l0g0/b-l072z-lrwan1/configs/sx127x/defconfig

@@ -37,7 +37,7 @@ CONFIG_MAX_TASKS=8
 CONFIG_MAX_WDOGPARMS=2
 CONFIG_NFILE_DESCRIPTORS=6
 CONFIG_NFILE_STREAMS=6
-CONFIG_NPTHREAD_KEYS=0
+CONFIG_TLS_NELEM=0
 CONFIG_NSH_ARCHINIT=y
 CONFIG_NSH_BUILTIN_APPS=y
 CONFIG_NSH_FILEIOSIZE=64