ARC: Fix CONFIG_STACKDEPOT

Enabling CONFIG_STACKDEPOT results in the following build error.

arc-elf-ld: lib/stackdepot.o: in function `filter_irq_stacks':
stackdepot.c:(.text+0x456): undefined reference to `__irqentry_text_start'
arc-elf-ld: stackdepot.c:(.text+0x456): undefined reference to `__irqentry_text_start'
arc-elf-ld: stackdepot.c:(.text+0x476): undefined reference to `__irqentry_text_end'
arc-elf-ld: stackdepot.c:(.text+0x476): undefined reference to `__irqentry_text_end'
arc-elf-ld: stackdepot.c:(.text+0x484): undefined reference to `__softirqentry_text_start'
arc-elf-ld: stackdepot.c:(.text+0x484): undefined reference to `__softirqentry_text_start'
arc-elf-ld: stackdepot.c:(.text+0x48c): undefined reference to `__softirqentry_text_end'
arc-elf-ld: stackdepot.c:(.text+0x48c): undefined reference to `__softirqentry_text_end'

Other architectures address this problem by adding IRQENTRY_TEXT and
SOFTIRQENTRY_TEXT to the text segment, so do the same here.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>