stm32l: Disable interrupts while running from flash
stm32l: Disable interrupts while running from flash

The curent code ends up creating a veneer for interrupt_enable/disable()
which isn't really needed (see below). By calling the interrupt code while
still running from flash we can avoid this.

I cannot see any problem with the current implementation, but it seems that
with this patch I also avoid an exception.

BUG=chrome-os-partner:20976
BRANCH=none
TEST=manual
Build EC and see code generated like this:

200029ec <iram_flash_write>:
200029ec:	b538      	push	{r3, r4, r5, lr}
200029ee:	460d      	mov	r5, r1
200029f0:	4604      	mov	r4, r0
200029f2:	f000 f83d 	bl	20002a70 <__interrupt_disable_veneer>
...

20002a4a:	f000 b809 	b.w	20002a60 <__interrupt_enable_veneer>
20002a4e:	bf00      	nop

20002a60 <__interrupt_enable_veneer>:
20002a60:	b401      	push	{r0}
20002a62:	4802      	ldr	r0, [pc, #8]	; (20002a6c <__interrupt_enable_veneer+0xc>)
20002a64:	4684      	mov	ip, r0
20002a66:	bc01      	pop	{r0}
20002a68:	4760      	bx	ip
20002a6a:	bf00      	nop
20002a6c:	080007f5 	.word	0x080007f5

20002a70 <__interrupt_disable_veneer>:
20002a70:	b401      	push	{r0}
20002a72:	4802      	ldr	r0, [pc, #8]	; (20002a7c <__interrupt_disable_veneer+0xc>)
20002a74:	4684      	mov	ip, r0
20002a76:	bc01      	pop	{r0}
20002a78:	4760      	bx	ip
20002a7a:	bf00      	nop
20002a7c:	080007f1 	.word	0x080007f1

With this patch the veneers go away.

Change-Id: Idfe173b4c8d45a142914b2388bcff8ba708c657c
Signed-off-by: Simon Glass <c00b0378376498bd9cd974c388df8854c0131d27@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/62243
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

akappy7/ChromeOS_EC_LED_Diagnostics,md5555/ec,akappy7/ChromeOS_EC_LED_Diagnostics,eatbyte/chromium-ec,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,longsleep/ec,fourier49/BZ_DEV_EC,alterapraxisptyltd/chromium-ec,fourier49/BZ_DEV_EC,coreboot/chrome-ec,eatbyte/chromium-ec,alterapraxisptyltd/chromium-ec,mtk09422/chromiumos-platform-ec,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,md5555/ec,coreboot/chrome-ec,gelraen/cros-ec,akappy7/ChromeOS_EC_LED_Diagnostics,thehobn/ec,longsleep/ec,gelraen/cros-ec,mtk09422/chromiumos-platform-ec,fourier49/BIZ_EC,longsleep/ec,alterapraxisptyltd/chromium-ec,gelraen/cros-ec,longsleep/ec,alterapraxisptyltd/chromium-ec,thehobn/ec,md5555/ec,gelraen/cros-ec,fourier49/BIZ_EC,mtk09422/chromiumos-platform-ec,coreboot/chrome-ec,fourier49/BZ_DEV_EC,eatbyte/chromium-ec,thehobn/ec,fourier49/BIZ_EC,mtk09422/chromiumos-platform-ec,thehobn/ec,md5555/ec,fourier49/BIZ_EC,coreboot/chrome-ec,eatbyte/chromium-ec,fourier49/BZ_DEV_EC