[components/drivers & bsp/stm32]fix kconfig syntax error and add rx buffer size config

bsp/stm32/stm32f103-dofly-lyc8/Kconfig

 mainmenu "RT-Thread Configuration"
 
-config $BSP_DIR
+config BSP_DIR
     string
     option env="BSP_ROOT"
     default "."
 
-config $RTT_DIR
+config RTT_DIR
     string
     option env="RTT_ROOT"
     default "../../.."
 
-config $PKGS_DIR
+config PKGS_DIR
     string
     option env="PKGS_ROOT"
     default "packages"

bsp/stm32/stm32f103-hw100k-ibox/Kconfig

 mainmenu "RT-Thread Configuration"
 
-config $BSP_DIR
+config BSP_DIR
     string
     option env="BSP_ROOT"
     default "."
 
-config $RTT_DIR
+config RTT_DIR
     string
     option env="RTT_ROOT"
     default "../../.."
 
-config $PKGS_DIR
+config PKGS_DIR
     string
     option env="PKGS_ROOT"
     default "packages"

bsp/stm32/stm32f746-st-disco/Kconfig

 mainmenu "RT-Thread Configuration"
 
-config $BSP_DIR
+config BSP_DIR
     string
     option env="BSP_ROOT"
     default "."
 
-config $RTT_DIR
+config RTT_DIR
     string
     option env="RTT_ROOT"
     default "../../.."
 
-config $PKGS_DIR
+config PKGS_DIR
     string
     option env="PKGS_ROOT"
     default "packages"

bsp/stm32/stm32f767-st-nucleo/Kconfig

 mainmenu "RT-Thread Configuration"
 
-config $BSP_DIR
+config BSP_DIR
     string
     option env="BSP_ROOT"
     default "."
 
-config $RTT_DIR
+config RTT_DIR
     string
     option env="RTT_ROOT"
     default "../../.."
 
-config $PKGS_DIR
+config PKGS_DIR
     string
     option env="PKGS_ROOT"
     default "packages"

bsp/stm32/stm32g071-st-nucleo/Kconfig

 mainmenu "RT-Thread Configuration"
 
-config $BSP_DIR
+config BSP_DIR
     string
     option env="BSP_ROOT"
     default "."
 
-config $RTT_DIR
+config RTT_DIR
     string
     option env="RTT_ROOT"
     default "../../.."
 
-config $PKGS_DIR
+config PKGS_DIR
     string
     option env="PKGS_ROOT"
     default "packages"

bsp/stm32/stm32l432-st-nucleo/Kconfig

 mainmenu "RT-Thread Configuration"
 
-config $BSP_DIR
+config BSP_DIR
     string
     option env="BSP_ROOT"
     default "."
 
-config $RTT_DIR
+config RTT_DIR
     string
     option env="RTT_ROOT"
     default "../../.."
 
-config $PKGS_DIR
+config PKGS_DIR
     string
     option env="PKGS_ROOT"
     default "packages"

components/drivers/Kconfig

@@ -20,7 +20,12 @@ if RT_USING_SERIAL
     config RT_SERIAL_USING_DMA
         bool "Enable serial DMA mode"
         default y
-endif    
+
+    config RT_SERIAL_RB_BUFSZ
+    int "Set RX buffer size"
+    default 64
+
+endif
 
 config RT_USING_CAN
     bool "Using CAN device drivers"
@@ -120,6 +125,7 @@ config RT_USING_PM
 
 config RT_USING_RTC
     bool "Using RTC device drivers"
+    select RT_USING_LIBC
     default n
 
     if RT_USING_RTC