rump: Remove deprecated ARM instruction

Substitute 'swpb' (swap byte) instruction with 'ldrexb/strexb', because 'swpb'
needs to be enabled explicitly by the kernel, which is done by neither HW or FOC.
When disabled, 'swpb' will cause an undefined instruction exception.

Issue #1048

dde_rump/patches/build.patch

@@ -1,5 +1,5 @@
 diff --git a/buildrump.sh b/buildrump.sh
-index f600b6a..e394b47 100755
+index f600b6a..f6bb302 100755
 --- a/buildrump.sh
 +++ b/buildrump.sh
 @@ -570,6 +570,16 @@ evaltools ()
@@ -55,3 +55,12 @@ index f600b6a..e394b47 100755
  	TOOLABI=''
  	case ${MACH_ARCH} in
  	"amd64"|"x86_64")
+@@ -918,6 +910,8 @@ evaltarget ()
+ 		MACHINE="evbarm"
+ 		MACH_ARCH="arm"
+ 		TOOLABI="elf"
++		EXTRA_CFLAGS='-march=armv7-a'
++		EXTRA_AFLAGS='-march=armv7-a'
+ 		probearm
+ 		;;
+ 	"sparc")

dde_rump/patches/lock.patch

@@ -0,0 +1,20 @@
+diff --git a/src/sys/arch/arm/include/lock.h b/sys/arch/arm/include/lock.h
+index c52a44f..3b4ba93 100644
+--- a/src/sys/arch/arm/include/lock.h
++++ b/src/sys/arch/arm/include/lock.h
+@@ -119,8 +119,13 @@ __swp(__cpu_simple_lock_t __val, volatile __cpu_simple_lock_t *__ptr)
+ 	return __rv;
+ #else
+ 	uint32_t __val32;
+-	__asm volatile("swpb %0, %1, [%2]"
+-	    : "=&r" (__val32) : "r" (__val), "r" (__ptr) : "memory");
++	__asm volatile(" 1:                  \n"
++	               "  ldrexb %0, [%2]    \n"
++	               "  strexb r0, %1, [%2]\n"
++	               "  teqeq  r0, #0      \n"
++	               "  bne 1b             \n"
++	               : "=&r" (__val32) : "r" (__val), "r" (__ptr)
++	               : "memory", "r0");
+ 	return __val32;
+ #endif
+ }