ARM: debug-ll: move DEBUG_LL_UART_EFM32 to correct Kconfig location

I accidentally move the DEBUG_LL_UART_EFM32 option when sorting all
other options alphanumerically, but it belongs into the same group
as DEBUG_LL_UART_8250 and DEBUG_LL_UART_PL01X.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 1dc93416 ("ARM: debug-ll: reorder Kconfig alphanumerically")