change interrupt num to 53
change stack size to 512 before system starup
add uart drivers
open msh
remain bug:
   uart just interrupt ones

	save sp to old thread
	clear rt_thread_switch_interrupt_flag
always enable interrupt after rt_hw_context_switch
judeg the type of interrupt in trap_entry, then call handler(Machine timer interrupt of Machine external interrupt)

	enable interrupt after return form rt_hw_context_switch

fix open timer intrrupt

	it will lead to interrupt again in interrupt

modified:   ../../libcpu/risc-v/e310/context_gcc.S
	change  ret to mret and switch to new task with mepc

[bsp] add new bsp for stm32l476-nucleo

[DeviceDrivers] improve sdio

[bsp] insert keep section .rti_fn* in GCC link file

[bsp] update k64 bsp to ksdk and add enet driver

 * add mkd5 support(template.uvprojx)

[bsp] fix bxcan.c inline bug

[bsp] update RCC initial for system

[DeviceDrivers]Fix continuous write page bug for spi_flash_at45dbxx driver

[DFS] To make sure the "console" device exist or not when initialize
console device.